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Innovative and advanced epitaxy

The symposium, co-organized with the EU COST action CA20116 OPERA ( takes an interdisciplinary and cross-community approach to key problems in epitaxy, including breakthroughs in challenging materials systems, new experimental and theoretical methods for the maturation of epitaxial materials, and novel functionalities for next-generation devices.


Today, material innovation is more vital than ever and needs to be not only more efficient and design-driven but also environment friendly as well as energy- and resource saving. The European epitaxy community is now at a turning point. Global challenges such as sustainability, information security, Smart Cities and the Internet of Things demand new technologies which can be enabled by advanced epitaxial materials. However, there are significant roadblocks to continued innovation in epitaxial materials, and these barriers are common across the wide range of maturity of the different materials classes:

  • a deep understanding of the basic processes allowing control of their synthesis and properties;
  • the development of hybrid material systems integrating multiple functionalities;
  • the material engineering to target specific properties in relation with identified applications;
  • the conversion of the scientific excellence into innovative solutions to establish disruptive technologies.

These topics, common to a large variety of epitaxial materials, whatever their form and synthesis techniques, constitute the essential prerequisites for their successful deployment into applications. In relationship with the EU COST Action OPERA, the symposium aims at bringing together scientists working in the field of epitaxy and push the merger of researchers 1) from traditionally separated scientific communities but having complementary knowledge and common interest, and 2) from academia and industry. It focuses therefore on innovative and advanced epitaxy, with the main objective to share ground-breaking theoretical or experimental researches on epitaxial materials, properties and devices, whatever the materials (III-V, III-N, group-IV, functional oxides, 2D-materials, novel metal or semi-metal compounds, dielectrics), their dimension (bulk, 2D-layer, 3D-shape, structured at micro- or nano-scales) and their growth technique (MBE, (MO)CVD, ALD, LPE, PLD...). New epitaxial combinations of materials will be highlighted, then opening the way towards next generation multi-functional devices. Thus, the symposium will be organized around the following research axes:

  1. Growth processes: surfaces, interfaces, wetting, kinetics, thermodynamics.
  2. Structure, stress and defects in epitaxial materials.
  3. Epitaxy of low-dimensional materials: substrate/epilayer interactions, nanostructures.
  4. Physical properties of epitaxial materials, relationships between structure, materials chemistry and targeted physical properties (e.g. optical, transport, ferroic and piezo properties, thermoelectricity, solar harvesting).
  5. Applications-oriented epitaxy: device architecture, doping, localized epitaxy.
  6. Advanced epitaxial materials for technological transfers in photonics, electronics, energy, communication / information, health, and environment; assessment of materials requirements.

Hot topics to be covered by the symposium:

  • Epitaxy of new materials: 2D-materials going beyond graphene, new alloys and compounds, oxides and free-standing oxide membranes, semi-metals and topological materials compatible with Si-based technology;
  • Epitaxy of new functional materials: hyperbolic materials, high Χ2 non linear materials, dielectric constant engineered materials, high-mobility materials, 2D/0D quantum-confined systems ...
  • Epitaxy of hybrid systems, combining materials with different properties: III-V/Si, oxides/Si or III-V, 2D/III-V or Si, III-V/metals or semimetals and oxide heterostructures;
  • New approaches of epitaxy in theory and experiment;
  • Epitaxy of innovative monolithic devices


Proceedings of the symposium will be published in thin solid films. A specific communication will be addressed to symposium attendees.

COST support:

The COST action OPERA may financially support the participation to the conference, especially for young researchers originating from target countries (ITC countries are Albania, Bosnia and Herzegovina, Bulgaria, Cyprus, Czech Republic, Estonia, Croatia, Georgia, Greece, Hungary, Lithuania, Latvia, Malta, Moldova, Montenegro, Poland, Portugal, Romania, Slovenia, Slovakia, Republic of North Macedonia, Republic of Serbia, Turkey and Ukraine). For more information about funding requests, please visit:

The OPERA COST Action aims to foster interdisciplinary collaborative research activities between the scientific communities and the industrial partners allowing maintaining European epitaxy at the topmost worldwide level of research and innovation, by disseminating new synthesis and characterization techniques, both for new/optimized nano- microscale growth tools, and new/optimized characterization tools. The action also aims at involving women scientists to highlight their career and favor their access to senior academic positions.

Confirmed invited speakers:

  • I. Berbezier (IM2NP, France)
  • F. Glas (C2N, France), “Modeling nucleation and growth statistics in semiconductor nanowires, based on in situ experiments”
  • A. Sanchez (University of Warwick, UK)
  • D. Babonneau (Institut P’, France), “Growth of self-aligned dichroic plasmonic nanostructures on amorphous surfaces”
  • M. Sawicka (Institute of high pressure Physics, Poland), “Electrochemical etching for blue laser diodes with nanoporous GaN cladding”
  • V. Zannier (Istituto Nanoscienze, Italy), “Free-standing InSb nanostructures: growth, morphology control and electrical characterization”
  • M. Jamet (CEA Grenoble, France), “Van der Waals epitaxy of two-dimensional transition metal dichalcogenides”
  • J. M. Lopes (PDI Berlin, Germany)
  • T. S. Jespersen (DTU, Denmark)
  • B. Daudin (CEA Grenoble, France), “AlN/GaN nanowire heterostructures for UV-C light emitting devices”
  • V. Marinova (IOMT-BAS, Bulgaria), “Graphene and 2D transition metal selenides: synthesis and characterizations”
  • E. Mensur Alkoy (Gebze Technical University, Turkey), “How Can the Electrocaloric Response in Ferroelectrics be Enhanced? Through Crystallographic Texture, or Point Defects, or Phase Coexistence?”

Scientific committee:

  • Marco Salvalaglio, TU Dresden (Germany)
  • Bogdan Ranguelov, Institute of Physical Chemistry, Laboratory of Electron Microscopy and Microanalysis (Bulgaria)
  • Marie-Ingrid Richard, ESRF (France)
  • Pierre Müller, CINaM (France)
  • Athanasios Dimoulas, NCSR-DEMOKRITOS, University of Athens (Greece)
  • Clément Merckling, IMEC, KU Leuven (Belgium)
  • Rafaella Calarco, CNR-IMM unit Rome (Italy)
  • Susana Cardoso Freitas, INESC, Lisboa (Portugal)
  • Peter Krogstrup, Niels Bohr Institute, Microsoft, Copenhagen, (Danemark)
  • Gertjan Koster, University of Twente, Enschede, (The Netherlands)
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09:00 Welcome Session & COST presentation C. Cornet, G. Bell, F. Leroy and A. Trampert    
Session 1 - Growth processes: surfaces, interfaces, wetting, kinetics, thermodynamics -1 : J.-N. Aqua
Authors : Frank Glas
Affiliations : Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 10 boulevard Thomas Gobert, 91120 Palaiseau, France

Resume : In principle, the lateral and axial dimensions of semiconductor nanowires (NWs) can be tailored easily. In particular, the length of a given NW section depends directly on growth duration. However, growth proceeds via the addition of biatomic monolayers (MLs) at the top of the NW. The formation of each ML is triggered by a single nucleation event, an intrinsically stochastic process. This is a key issue, since axial NW heterostructures, whether based on composition modulations or on alternating crystal structures in a single material, often require control at the ML level. Vapor-solid-liquid (VLS) NW growth provides a choice example of nucleation in a confined nanosize medium, the study of which is of basic interest while also opening prospects for minimizing nucleation-related randomness. In VLS, the MLs form at the interface between the NW stem and an apical liquid catalyst nanodroplet. In situ transmission electron microscopy (TEM) now allows one to study the formation of sequences of MLs at atomic resolution and in real time. This gives access to the kinetics but also to the statistics of nucleation and growth. Quite generally, two solid-liquid interface morphologies may exist, depending on the droplet contact angle. We focus on NWs of III-V materials, in particular GaAs. When the interface remains planar, growth material originates entirely from the liquid phase. Each ML cycle consists of three stages: (1) nucleation of a 2D island and fast formation of a fractional ML, (2) slower propagation of the ML until completion, (3) waiting time before the nucleation of the next ML. This is interpreted as indicating that, at nucleation, the droplet contains less than a ML worth of the volatile group V element, which forms the partial ML (stage 1), while at stage 2 new group V atoms brought steadily by the vapor flux serve to extend the ML and not to enrich the liquid, which remains at equilibrium with the solid. The propagation and waiting times of long sequences of monolayers were measured by in situ TEM at three growth temperatures, in a single GaAs NW. The process was modeled and the statistics of the characteristic times were computed numerically and analytically. Quantitative comparisons are made and the parameters governing the nucleation rate are estimated. We show that, at low temperature (without desorption from the liquid), a non-vanishing stage 2 may produce a self-regulated quasi-deterministic growth regime whereby, despite the stochasticity of nucleation, each ML cycle tends to last exactly the same time. This could be very beneficial in terms of growth control, with the perspective of setting precisely the length of a NW section in a standard growth setup, without recourse to direct observation. We have thus determined the domain of existence of the incomplete ML regime in terms of temperature, NW radius and external growth flux. To this end, we calculated the density of probability of the nucleation probability (as a function of group V concentration in the liquid), which allows us to determine the distributions of all characteristic times. The second possible interface morphology is 'truncated'. A wedge of the solid NW is then missing at the periphery of its top facet and the wedge volume oscillates in phase with the ML cycle. Growth is then partly fed by the transfer to the ML of part of the already grown NW material. We will discuss why this happens and how the statistics of nucleation and propagation may be affected by this extra growth channel.

Authors : D. Babonneau, E. De Los Santos Vazquez, S. Camelio, S. Rousselet, F. Pailloux, G. Abadias, M. Bayle, B. Humbert
Affiliations : D. Babonneau Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Département Physique et Mécanique des Matériaux, 86073 Poitiers, France; E. De Los Santos Vazquez Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Département Physique et Mécanique des Matériaux, 86073 Poitiers, France, and Institut des Matériaux Jean Rouxel, Université de Nantes, UMR 6502 CNRS, 44322 Nantes Cedex 3, France; S. Camelio Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Département Physique et Mécanique des Matériaux, 86073 Poitiers, France; S. Rousselet Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Département Physique et Mécanique des Matériaux, 86073 Poitiers, France; F. Pailloux Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Département Physique et Mécanique des Matériaux, 86073 Poitiers, France; G. Abadias Institut Pprime, UPR 3346 CNRS-Université de Poitiers, Département Physique et Mécanique des Matériaux, 86073 Poitiers, France; M. Bayle Institut des Matériaux Jean Rouxel, Université de Nantes, UMR 6502 CNRS, 44322 Nantes Cedex 3, France; B. Humbert Institut des Matériaux Jean Rouxel, Université de Nantes, UMR 6502 CNRS, 44322 Nantes Cedex 3, France;

Resume : Recent applications of noble and non-noble metal nanostructures with tunable plasmonic properties (e.g. in nanoscale photonics, photovoltaics, imaging, sensing, biology and medicine, etc.) demand a full control of their morphology (size and shape), organization, and composition over large areas up to several tens of cm2. However, still to this day, technical challenges make it difficult to achieve the production of self-assembled plasmonic nanostructures using high-throughput lithography-free methods. Indeed, self-organization approaches including PVD growth and solid-state dewetting of metal thin films suffer from inherent limitations to generate randomly oriented or highly directional dichroic nanostructures at low adatom mobility or high adhesion coefficient. This is especially the case for aluminum and refractory transition metal nitrides, which have recently emerged as promising alternatives to conventional, noble metal-based plasmonic materials such as Ag and Au. In this presentation, we will show that periodic nanoripple patterns produced by low-energy ion-beam sputtering of insulating amorphous surfaces can be used as templates to fabricate self-aligned nanoparticles and nanowires by oblique-angle deposition of Ag [1,2], Au [3], Al [4], TiN or ZrN [5]. Based on experimental and numerical investigations of their far-field and near-field behavior, we will show that these systems possess original dichroic properties, reflected in a polarization-dependent excitation of their surface plasmon resonances, which might be tailored and exploited for various applications such as surface-enhanced Raman scattering [2] or second-harmonic generation [5]. [1] L. Simonot, F. Chabanais, S. Rousselet, F. Pailloux, S. Camelio, D. Babonneau, Evolution of plasmonic nanostructures under ultra-low-energy ion bombardment, Appl. Surf. Sci. 544 (2021) 148672 [2] S. Camelio, D. Babonneau, E. Vandenhecke, G. Louarn, B. Humbert, Linear chains of Ag nanoparticles embedded in dielectric films for SERS applications in analytical chemistry, Nanoscale Adv. 3 (2021) 6719?6727 [3] E. Soria, P. Gomez-Rodriguez, C. Tromas, S. Camelio, D. Babonneau, R. Serna, J. Gonzalo, J. Toudert, Self-assembled, 10 nm-tailored, near infrared plasmonic metasurface acting as broadband omnidirectional polarizing mirror, Adv. Opt. Mater. 8 (2020) 2000321 [4] A. Fafin, S. Camelio, F. Pailloux, D. Babonneau, Surface plasmon resonances and local field enhancement in aluminum nanoparticles embedded in silicon nitride, J. Phys. Chem. C 123 (2019) 13908?13917 [5] D. Babonneau, S. Camelio, G. Abadias, D. Christofilos, I. Arvanitidis, S. Psilodimitrakopoulos, G. M. Maragkakis, E. Stratakis, N. Kalfagiannis, P. Patsalas, Self-assembled dichroic plasmonic nitride nanostructures with broken centrosymmetry for second-harmonic generation, ACS Appl. Nano Mater. 4 (2021) 8789?8800

10:30 Coffee Break    
Session 1 - Growth processes: surfaces, interfaces, wetting, kinetics, thermodynamics-2 : F. Glas
Authors : Dong Yeong Kim, Thomas J. Smart, Hans Boschker, Sander Smink, Lena Majer, Jochen Mannhart, and Wolfgang Braun
Affiliations : Max Planck Institute for Solid State Research; Max Planck Institute for Solid State Research; Epiray; Max Planck Institute for Solid State Research; Max Planck Institute for Solid State Research; Max Planck Institute for Solid State Research; Max Planck Institute for Solid State Research

Resume : The synthesis of highly pure and stoichiometric films and heterostructures is essential for many areas of science and for applications. Thermal laser epitaxy (TLE) is a novel film growth technique that can achieve this goal. TLE uses continuous laser beams to both thermally vaporize pure metal sources and heat the substrate. TLE opens new possibilities for epitaxy by providing ultrapure molecular fluxes and allowing the use of adsorption-limited growth modes at very high substrate and source temperatures, as well as the possibility of deposition in highly reactive atmospheres. In the presentation, we will describe the growth of a variety of films by TLE. These include ultraclean metal and semiconductor films deposited in ultra-high vacuum, and a spectrum of binary oxide films grown by evaporating pure elemental sources in oxidizing atmospheres. In addition, the first results of using TLE for the growth of carbides and nitrides will be presented. We will also discuss the advantages of TLE in opening up the possibility of using a wide range of source elements, extreme substrate temperatures, and high-pressure atmospheres, also of reactive gases, in the epitaxial growth process. These now accessible parameter ranges provide new opportunities for the epitaxial growth of ultra-high purity films and heterostructures.

Authors : M. Stachowicz1, S. Magalhaes2, E. Przezdziecka1, J.M. Sajkowski1, A. Pieni??ek1, E. Alves2, A. Kozanecki1
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46 PL-02-668 Warsaw, Poland 2 Centro Tecnológico Nuclear, Instituto Superior Técnico, Universidade de Lisboa, P-2686953 Sacavém, Portugal

Resume : The wide gap II?VI semiconductors as the growth techniques became more mature, have become of increasing technological importance, in particular for the development of light emitting diodes and lasers operating in the visible and ultraviolet region. Such devices contain heterojunctions and active areas based on quantum structures. Because of the large concentration of dopants, the gradients are present and therefore interdiffusion of the matrix components during growth and processing is of inevitable concern. Such interdiffusion occurrence during the growth or subsequent processing can lead to composition changes of the interface and quantum structure profiles and the strain distribution, modifying the band gap configuration and consequently the device parameters. A quantitative knowledge of the interdiffusion parameters is, therefore, essential. An interesting feature of ZnO, which is II-VI group semiconductor, is the possibility to tune its band gap by substituting bivalent metals like Cd in the place of Zn. CdO is a compound semiconductor with direct band gap of 2.3 eV, and Cd substitution for Zn can lead to narrowing of Zn1-xCdxO band gap depending on the Cd concentration. In this work, we present the result of an atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL), cathodoluminescence (CL), and Rutherford backscattering spectroscopy (RBS) study of the temperature induced intermixing in ZnO/Zn1-xCdxO layers. Conducted experiments delivered information on structural and spectroscopic properties of subjected structures, as well as interdiffusion range and coefficient for different Cd compositions. The obtained concentrations of MBE grown ZnCdO thin films were established up to 6.7% in as grown ZnCdO layers. Assessed value of diffusion efficiency, based on fitting experimental data accordingly to one dimensional Fick?s equation, was up to Deff(Cd)=0.67 cm2/s after annealing at 650 oC. The range of cadmium diffusion was established to be up to ld(Cd)= 9±2 nm at the alluded annealing temperature. Established dislocation density, present in the subjected structures, additionally promotes interdiffusion of Cd elements, especially in the ionic crystals [1]. [1] M.A.N. Nogueira, W.B. Ferraz, A.C.S. Sabioni, Diffusion of the 65Zn radiotracer in ZnO polycrystalline ceramics, Mater. Res., 6 (2003) 167. Acknowledgements The work was partly supported by the NCN project DEC-2018/28/C/ST3/00285, No. 2019/35/B/ST8/01937, and No. 2021/41/B/ST5/00216

Authors : T. Ben1, V. Braza1, S. Flores1, A. Gallego Carro2, L. Stanojevi?2, Malte Schwarz2, D. Fernandez-Reyes1, ?. Ga?evi?2, J.M. Ulloa2 and D. Gonzalez1
Affiliations : 1 University Research Institute on Electron Microscopy & Materials, (IMEYMAT), Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain 2 Institute for Optoelectronic Systems and Microtechnology (ISOM), Universidad Politécnica de Madrid, Avda. Complutense 30, 28040 Madrid, Spain

Resume : To achieve the theoretical limiting efficiency of energy conversion in multijunction monolithic solar cells (MJSCs), a combination of subcells of different materials with suitable lattice constants and bandgap energies must be designed. GaAsSb/GaAsN short-period superlattices (SLs), with type II bandgap alignment, could be the ideal candidate to implement as a subcell with bandgap energy between 1.0-1.15 eV in the standard GaAs/Ge-based MJSC. Nevertheless, as yet the photovoltaic performance of these structures are far from the expected one. This is partly due to the fact that the experimental Sb profiles in these SLs differ greatly from the nominal square-wave design due to the strong segregation of Sb in the GaAsN layer, thus distorting the expected type-II emission. This phenomenon is aggravated in the case of very short-period SLs as they exhibit shark-fin wave profiles that even need many periods to reach the steady-state condition. However, these SLs are the ideal ones for providing an optimal balance between high photon absorption and high carrier extraction. To approach the desired photovoltaic efficiencies, our research has focused on the improvement of the internal interfaces in terms of abruptness and roughness. For this purpose, different strategies based on growth interruptions have been proposed, such as exposing the surface to different Sb/As fluxes before (Sb soaking) and/or As fluxes after (Sb desorption) deposition of the GaAsSb layer. In this work, we have evaluated the interface quality in GaAsSb/GaAsN SLs grown by molecular beam epitaxy after applying different interruption timing approaches with Sb soaking and Sb desorption at the beginning and at the end of the growth of each GaAsSb layer, respectively. The structural quality was analyzed by different methodologies in a FEI Titan Cubed3 Themis double aberration-corrected scanning transmission electron microscope. The solar cell devices were made by standard processing techniques and analysed by voltage-dependent photocurrent spectroscopy. The results show that both Sb soaking and desorption processes lead to a significant improvement of both the slope of the composition gradient and the surface roughness at both interfaces. The improvement of the slope is more significant during soaking, saturating after 20 s, than in desorption, which stabilizes after 10 s. However, surface roughness stronger decreases at the upper interface than at the lower one. The changes in the compositional profiles have been discussed in the framework of the three-layer fluid kinetic segregation model. It has been found that there is a progressive decrease in the ratio of exchange energies, which has been associated with gradual changes in the surface reconstruction of the floating Sb layer. The application of these strategies has produced a strong impact on the performance in single junction devices solar cell, with an overall 325% increase of the conversion efficiency over the uninterrupted case.

Authors : Elzbieta Pach1, Jordi Aguilar1, Daniel Sanchez2, Lavinia Saltarelli1, Diana Garcia1, Albert Queralto1, Kapil Gupta1, Eduardo Solano3, Marc Malfois3, Xavier Obradors1, Teresa Puig1
Affiliations : 1Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, 08193 Cerdanyola del Vallès, Spain; 2 GRMT, Department of Physics, University of Girona, E17071-Girona, Spain; 3 NCD-Sweet beamline, ALBA synchrotron light source, 08290Cerdanyola del Vallès , Spain

Resume : Investigation on the preparation of efficient and flexible high temperature superconducting materials (HTS) is one of the puzzles to be solved for the Energy Transition goal. One of the important parts of this development is focused on the cost-effective, scalable methods of synthesis of such materials. Nowadays, HTS based on REBa2Cu3O7 (RE=Y or Rare Earth, REBCO) are manufactured as long, flexible conductors deposited on metallic substrates using thin film technologies, the so-called coated conductors (CC), which are rather expensive. Our approach is to use an innovative method, called Transient Liquid Assisted Growth (TLAG) [1], a non-equilibrium process based on epitaxial crystallization from a transient melt at very high growth rates (100 nm/s, 100 times larger than conventional methods). This process is compatible with low cost, scalable chemical solution deposition methods and allows to grow high temperature epitaxial superconducting films. However, in order to achieve a deep understanding of such a fast growth process of REBCO films, determine the phases´ evolution and the kinetic phase diagrams that would permit to better control their properties, a new methodology had to be developed. This goal is being achieved through fast acquisition of in-situ X-Ray diffraction data during the TLAG process at the NCD-Sweet synchrotron beamline of ALBA light source in Spain. For that purpose, a unique portable system was developed using a fast heating XRD furnace with controlled atmosphere capable to tune temperature up to 1000 ºC and total pressures from 10-5 bar to 1 bar with controlled oxygen partial pressure and flow rate synchronized with simultaneous acquisition of 2D XRD images at 100 ms/image at 18 keV. Additionally, the system allows for simultaneous analysis of the volatiles with mass spectrometry and in-situ electrical conductivity that permits to follow the phase transformation from the insulating precursor phases to the metallic superconductor phase at the growth conditions. The ultrafast process of TLAG required very fast time responses of all the systems and accurate time synchronizations. Results on the epitaxial nucleation and growth mechanism of the REBCO phase on STO single crystals and metallic substrates, and TLAG phase evolutions process will be discussed. [1] L. Soler et al, Nature Communications,11, 344 (2020) * Research funded by ERC-2014-ADG-669504 and CSIC PTI-TRANSENER+

Authors : M. A. Wohlgemuth, U. Trstenjak, A. Sarantopoulos, F. Gunkel, R. Dittmann
Affiliations : Peter-Grünberg-Institut 7, Forschungszentrum Jülich GmbH; JARA-FIT, RWTH Aachen

Resume : Remote epitaxy, in which the thin film is seeded by the underlying substrate through a 2D-material buffer layer, allows to unclamp epitaxial films from the substrate, while maintaining their structural relationship. This potentially lifts some of the limitations of classical epitaxy, where only materials with similar lattice parameters and crystal structure can be combined and where substrate-clamping can lead to strain and distortions of the thin film lattice. Thus, remotely controlled growth can broaden the choice of material systems used for epitaxy. In addition, remote epitaxy can be used to exfoliate layers from the restrictive substrate, creating a freestanding membrane, which can be transferred to any host substrate or electronic device, making this method of great interest for many research fields. Graphene has been previously used as 2D buffer layer to remotely control the film-substrate interaction during growth via pulsed laser deposition (PLD). In contrast to semiconductor epitaxy, where often atmospheres in the low-pressure regime are applied, the epitaxy of functional complex oxides typically requires high oxygen pressures to ensure low-defect concentration and sufficient oxidation. In such conventional oxygen atmospheres, however, graphene will be oxidized and thereby damaged during the growth of the oxide thin film. The present study shows a way to maintain the buffer layer as well as the desired thin film stoichiometry during homoepitaxial growth of strontium titanate (SrTiO3) on graphene-covered substrates. This was achieved by optimization of the competing effects of kinetic impact during growth (controlled by the absolute growth pressure), oxidation of the buffer layer (controlled by the oxygen partial pressure) and resulting thin film stoichiometry. We investigated the growth of SrTiO3 in vacuum, oxygen and argon atmospheres. In vacuum, the laser spot size was changed to reduce the kinetic energy of incoming species impinging on the graphene-covered substrate. The resulting thin films were characterized with respect to their surface morphology, crystal structure and stoichiometry. The quality of the graphene was investigated by Raman spectroscopy. We find that graphene as bilayer is more durable than as monolayer, which is completely destroyed even at the lowest oxygen pressures. In vacuum and in argon atmosphere, the graphene buffer layer can be preserved but is partially damaged, as indicated by a rising G band in the Raman spectroscopy, which is closely related to the defect density of graphene. In vacuum a smaller laser spot size led to less defective buffer layers, whilst in argon atmosphere the lowest G bands were found for the highest partial pressure. Our results show that gentle growth kinetics and absence of oxygen improves the quality of complex oxides remote epitaxy.

Authors : V. Fuentes b, S. Martin-Rio b, Z. Konstantinovi? a , C. Frontera b, Ll. Balcells b, B. Martínez b, A. Pomar b
Affiliations : a Center for Solid State Physics and New Materials, Institute of Physics Belgrade, Serbia b Instituto de Ciencia de Materiales de Barcelona, ICMAB-CSIC, 08193 Spain

Resume : In recent years, there is an increased interest for the 5d oxides due to their stronger Spin Orbit Coupling (SOC) in comparison with their 3d analogous. The increment in the SOC is responsible for the arise of a variety of exotic properties in this group of oxides boosting, therefore, its potential for basic and applied research. In particular, SrIrO3 has emerged as a suitable candidate as spin sinker in ferromagnetic/SOC-metallic bilayers, allowing to study spin injection in all-oxide heterostructures. Moreover, physical properties in transition metal oxides thin films may be finely tuned by a wise choice of growth conditions during deposition process. In this respect, SIO thin films exhibit a metal-insulator transition that may be tuned by thickness or epitaxial strain. [1] In the present work, we have explored the influence of growth kinetics on the physical properties of SrIrO3 thin films and their influence on spin injection. We have observed that by modifying the growth conditions a competition between different growth modes occurs, leading to the decoration of the film surface in the form of ordered pits. Interestingly, the physical properties of the nanostructured films are clearly modified, with the occurrence of metal-insulator transition shifted to higher thicknesses. These results may be analyzed in terms of strain relaxation mechanisms. We will also present results of spin pumping experiments through Ferromagnetic Resonance Spectroscopy in La2/3Sr1/3MnO3/SIO bilayers. We will compare spin injection in those all-oxide structures with previous results in manganite-based bilayers with Pt as cap layer [2]. We will analyse Inverse Spin Hall Effect measurements and we will discuss the influence of the achieved surfaces in the spin-mixing conductance. [1] See, e.g., V. Fuentes et al, ACS Applied Electronic Materials 1, 1981 (2019) and references therein. [2] S. Martin-Rio et al., J Mat Chem C, 10.1039/d2tc00048b

12:30 Lunch Break    
Session 1 - Growth processes: surfaces, interfaces, wetting, kinetics, thermodynamics-3 : P. Müller
Authors : Thomas Sand Jespersen
Affiliations : Department of Energy Conversion and Storage Technical University of Denmark

Resume : Selective area growth of semiconductor nanostructures, where areas of crystal growth are designed using pre-growth semiconductor processing, is a promising route for realizing semiconductor nanostructures beyond the capabilities of conventional vapour-liquid-solid growth: Multi-terminal branched quantum devices, large scale networks of coupled nanostructures, and in general enables scaling of device architectures. In addition, SAG provides the possibility to design large-areas SAG semiconductors used as classical building blocks for building on-chip electronics to control and address quantum measurements. Here we discuss recent results in SAG growth of nanostructures and the realization of multiplexer control electronics allowing a new degree of statistical significance in characterization of semiconductor nanostructures.

Authors : H. Khemliche, A.R. Allouche, A. Mukherjee, A. Momeni, E. M. Staicu Casagrande
Affiliations : Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d?Orsay, 91405, Orsay, France

Resume : Design and development of high quality thin-layer heterostructures with controlled properties are major challenges for nanoscience and nanotechnology. The ?materials by design? approach speeds up the design of this type of materials according to desired properties. The second critical step is to produce the thin layers in a controlled manner so that the expected properties are met. The development of efficient growth processes requires sensitive and discriminating tools, capable of providing the most complete information on the layer properties during growth. A new technique, based on grazing incidence diffraction of fast (near 1 keV) helium atoms and called GIFAD (Grazing Incidence Fast Atom Diffraction), provides access to a wealth of properties on any type of material (inorganic, organic, conductor, insulator, etc.). GIFAD probes, in reciprocal space, the electron density profile at distances comparable to that of an STM or AFM tip, therefore in regions perfectly relevant for adsorption phenomena. A basic treatment of the diffraction pattern thus provides access to the electronic corrugation. Due to the very soft nature of the grazing He-surface interaction, GIFAD makes it possible to monitor the growth of an organic layer over long periods without any damage. Another unique advantage of GIFAD, compared to electron or X-ray diffraction, is the capacity to directly identify phase transitions, at the scale of a monolayer, without apparent change of symmetry. These transitions, which correspond to subtle changes (atomic displacement, chemical composition, charge transfer, etc.) within the lattice, translate into variations of the relative intensity of the Bragg peaks. With such a high sensitivity to growth mode, organization dynamics, crystalline structure and defect density, GIFAD should offer a better control over the growth process, in particular by providing reliable end point detection, either in terms of thickness in layer-by-layer mode or through a specific crystalline phase. In addition to studies on the growth and structure of III-V semiconductors, we will illustrate the capabilities of GIFAD on more flexible and fragile materials, such as hybrid organic/inorganic compounds and their precursors. With the recent advent of a high-pressure version, GIFAD should be compatible with all vacuum deposition techniques: Molecular Beam Epitaxy, Pulsed Laser Deposition, Plasma Magnetron Sputtering, Chemical Vapor Deposition, etc.

Authors : Jean-Noel AQUA [1], Zouhour BEN JABRA [2], Mathieu ABEL [2], Isabelle BERBEZIER [2], Mathieu KOUDIA [2], Antoine RONDA [2], Filippo FABBRI [3], Adrien MICHON [4], Paola CASTRUCCI [5], Maurizio DE CRESCENZI [5], Holger VACH [6].
Affiliations : [1] INSP, Sorbonne Université, CNRS, Paris, France [2] IM2NP, Aix-Marseille Université, CNRS, Marseille, France [3] NEST, Istituto Nanoscienze ? CNR, Pisa, Italy [4] CRHEA, Université Co?te d?Azur, CNRS, Valbonne, France [5] Dipartimento di Fisica, Universita di Roma Tor Vergata, Roma, Italy [6] LPICM, CNRS, Ecole Polytechnique, IP Paris, Palaiseau, France

Resume : The promising way for integration of 2D materials (2DM) is their production by epitaxy that is a technological lock for any potential industrial application of these systems. The synthesis of silicene and germanene by epitaxy has been first reported on metallic substrates. However, their properties were found to be strongly affected by the coupling with their substrate and mixing effects between the substrate and the 2D film were revealed under certain conditions. In addition, fabrication of functional electronic devices necessarily requires non-metallic supports. One possibility is to introduce a buffer layer for decoupling the 2D adlayer from the substrate, as it has been recently proposed. Recent experiments concerning the epitaxial growth of Si on highly oriented pyrolytic graphite revealed the possibility to grow either 2D flakes with rather small sizes, or dewetted fractal islands. In any case, the understanding and control of the epitaxial growth of 2D materials is largely insufficient, and today?s progress is limited by the lack of wafer-scale uniform growth that requires further investigation of dynamical mechanisms. To progress in this direction, we developed kinetic Monte-Carlo (kMC) simulations of the epitaxy of silicene on various substrates (graphene, Ag(111) ?). First principles-calculations have revealed the stability of some structures, but the dynamical description of their growth that dictates the resulting shapes is still insufficient. The challenge is to simulate out-of-equilibrium systems of sufficient size (typically of the order of a hundred nanometers) yet incorporating atomic details, over sufficiently long times (typically of the order of a minute or more) yet describing atomic events (diffusion, incorporation, exchange?). Recent experiments revealed the possibility to grow large flakes of silicene on a graphene substrate of high quality. We will show how the growth kinetics may rule the resulting shapes and the possibility to control the quality of the 2D materials.

15:15 Coffee Break    
Session 2 - Structure, stress and defects in epitaxial materials-1 : P. Müller
Authors : Ebru MENSUR ALKOY

Resume : The ferroelectrics has still been a good candidate for the electrocaloric effect (ECE) to develop environmentally friendly cooling alternative systems. Most of the time, the ECE is very small in ferroelectrics. However, giant electrocaloric response was reported in several organic and inorganic relaxor ferroelectric systems, thus, initiating an intense research effort on this phenomenon. There are some strategies for improving EC response in ferroelectrics such as; Compositional Modification, i.e. doping, selecting compositions with phase coexistence, or Utilization of Anisotropy, i.e. using single crystals with specific orientations, texturing polycrystalline ceramics, etc. This talk will discuss the main drivers and their relative effects on the enhancement of EC performance in PMN-PT, PLZT lead-based lead-free BZT and BCZT systems mainly in the light of texture. These ferroelectrics systems were especially chosen for their relaxor behavior or their position in the phase diagram which shows phase co-existence such as triple points etc.

Authors : Tadeá? Hanu?, Thierno Mamoudou Diallo, Andreas Ruediger, Gilles Patriarche, Pascal Brault, Abderraouf Boucherif
Affiliations : Tadeá? Hanu? 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada ;Thierno Mamoudou Diallo 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada ;Andreas Ruediger 3: Nanoelectronics-Nanophotonics INRS-EMT, 1650, Boulevard Lionel-Boulet, Varennes, J3X 1S2 QC, Canada ;Gilles Patriarche 4: Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies (C2N), Palaiseau, 91120, France ;Pascal Brault 5: GREMI, Groupe de Recherches sur l?Énergétique des Milieux Ionisés UMR7344, CNRS/Université d'Orléans, 14 rue d'Issoudun, BP 6744, 45067 Orléans Cedex 2, France ;Abderraouf Boucherif 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada

Resume : The discovery of graphene sparked an overwhelming scientific and technological interest in electronics, quantum devices and optoelectronics, due to its remarkable mechanical, optical, and thermal properties [1]. Its integration with semiconductor materials (Gr. IV, III-V, III-N, etc.) with even higher potential, has started the development of whole new generation of functional hybrid heterostructures, enabling heterointegration of dissimilar materials and layer transfer. However, while the direct integration of 2D materials on 3D materials by transfer or Van der Waals epitaxy (VdWE) has been well established, the epitaxial growth of single-crystalline semiconductor materials (3D) on 2D heterostructures has been very challenging. This is mainly due to the low surface energy of the graphene and Van der Waals bonding between 2D graphene and 3D bulk material [2], creating harsh condition for nucleation and crystal orientation. Even though, remote epitaxy has been proven to enable the growth of single-crystalline films of various compound materials on graphene substrates [3,4]. This is made possible by polar interactions, thought graphene layer, between the substrate and epitaxial layer. However, its use excludes all the applications involving elemental (non-polar) materials such as silicon (Si) and germanium (Ge). Therefore, engineering the surface energy of graphene in order to improve its reactivity is one of the most interesting topics in material science. For this reason, we have implemented a new approach of graphene engineering based on plasma treatment to alleviate the aforementioned challenges. In fact, it is reported that light plasma treatment can be used to introduce defects in the graphene lattice, thereby improving its surface reactivity and adhesion with other materials [5,6]. Nevertheless, the exact nature of the defects and their effects on crystal growth is still a debate. In this study, we report the effect of plasma treatment on single layer graphene (SLG) and its influence on the nucleation of Ge on SLG. The effect of plasma treatment duration was also studied. The quality and the chemical bonding of the treated SLG were investigated using, respectively, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The experimental data showed clear evidence of defect introduction in the plasma treated SLG. The induced defects are found to be mainly pinholes and dangling bonds. Moreover, the presence of these defects was demonstrated by the increasing of nuclei density during the nucleation of Ge on the treated SLG. These observations provide a clear corroboration for the role played by the induced defects in the nucleation process, the improvement of surface energy and the reactivity of graphene. Furthermore, the crystallinity of the fully-grown Ge layers on treated SLG is investigated using electron backscatter diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). These findings provide new insights on plasma-induced defects in SLG and open a new route for growth of single-crystalline semiconductors including elemental materials (Si and Ge) on SLG for hybrid functional devices. [1] Novoselov, K., Fal?ko, V., Colombo, L. et al. Nature 490, 192?200 (2012) [2] Alaskar, Y., et al., Adv. Funct. Mater. (2014). [3] Kim, Y., et al., Nature 544, 340?343 (2017) [4] Kong, W., et al., Nature Mater 17, 999?1004 (2018) [5] K. Chu, J. Wang, Y.-p. Liu, Y.-b. Li, C.-c. Jia, H. Zhang, Carbon, 143, pp. 85-96, (2019). [6] Y.J. Shin, et al., Langmuir 26 (6), 3798-3802, (2010)

Authors : Nicolas Paupy, Bouraoui Ilahi, Tadeá? Hanu?, Valentin Daniel, Roxana Arvinte, Alex Brice Poungoué Mbeunmi, Alexandre Heintz, Thierno Mamoudou Diallo, Zakaria Oulad Elhmaidi, Richard Arès, Abderraouf Boucherif
Affiliations : Nicolas Paupy 1,2; Bouraoui Ilahi 1,2; Tadeá? Hanu? 1,2; Valentin Daniel 1,2; Roxana Arvinte 1,2; Alex Brice Poungoué Mbeunmi 1,2; Alexandre Heintz 1,2; Thierno Mamoudou Diallo 1,2; Zakaria Oulad Elhmaidi 1,2; Richard Arès 1,2; Abderraouf Boucherif 1,2 1-Institut Interdisciplinaire d?Innovation Technologique (3IT), Université de Sherbrooke, 3000 boulevard Université, Sherbrooke, J1K 0A5 Québec, Canada 2-Laboratoire Nanotechnologies Nano systèmes (LN2) ? CNRS UMI-3463 Institut Interdisciplinaire d?Innovation Technologique (3IT), Université de Sherbrooke, 3000 boulevard Université, Sherbrooke, J1K 0A5 Québec, Canada

Resume : III-V multijunction solar cells, currently hold the highest reported efficiency [1]. Meanwhile, their high production cost prohibits their large-scale commercialization for terrestrial use. Furthermore, to fulfill their accurate use in space application, their weight needs to be considerably reduced. Accordingly, for III-V cells on Ge substrate, the thickness of the substrate is typically around 200 µm [2], whereas few µm would be enough to maintain the performance of the cell [3]. It is therefore important to find a scalable and cost-effective approach for layer separation and reuse of the Ge substrate allowing to reduce both solar cells wight and cost. In this work [4], we demonstrate for the first time the epitaxial growth of wafer scale detachable epi-ready Ge template on 4-inch porous Ge (PGe) substrate [5], suitable for the growth of III-V materials and devices. Indeed, monocrystalline Ge epitaxial template with very low surface roughness (below 1 nm and comparable to the epi-ready bulk substrate) has been successively grown on PGe wafer. During the epitaxial growth, the PGe layer undergoes morphological transformation leading to pillars formation serving as weak interface allowing defect free layer separation. High resolution transmission electron microscopy study revealed that the detachable membrane exhibits excellent monocrystalline properties and maintains the same crystalline orientation and substrate miscut as the mother substrate which is required for III-V multijunction solar cell growth. Indeed, to demonstrate the viability of our detachable Ge template for solar cell growth, good quality GaAs layer has been successively grown. Our findings pave the way to a scalable and cost-effective approach towards III-V/Ge heterostructures separation and substrate reuse which brings an important technological brick for disruptive epitaxial devices such as solar cells and optoelectronics. References: [1] J. F. Geisz et al., « Six-junction III?V solar cells with 47.1% conversion efficiency under 143 Suns concentration », Nat. Energy, vol. 5, no 4, p. 326?335, avr. 2020, doi: 10.1038/s41560-020-0598-5. [2] A. Boucherif, G. Beaudin, V. Aimez, et R. Arès, « Mesoporous germanium morphology transformation for lift-off process and substrate re-use », Appl. Phys. Lett., vol. 102, no 1, p. 011915, janv. 2013, doi: 10.1063/1.4775357. [3] D. J. Aiken, « InGaP/GaAs/Ge multi-junction solar cell efficiency improvements using epitaxial germanium », in Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialists Conference - 2000 (Cat. No.00CH37036), Anchorage, AK, USA, 2000, p. 994?997. doi: 10.1109/PVSC.2000.916053. [4] N.Paupy, A. Chapotot, T. Hanu? et al, Wafer-scale detachable monocrystalline Ge nanomembranes for the growth of III-V materials and substrate reuse ? to be published [5] T. Hanu? et al, Electrochemical etching modulation and nondestructive characterization: a platform for wafer scale homogeneous porous Ge layers ? to be published

Authors : Roman Stoklas, Stanislav Hasenöhrl, Edmund Dobro?ka, Filip Gucmann, Jan Kuzmík
Affiliations : Institute of Electrical Engineering, SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovakia

Resume : Indium nitride (InN) represent an important group III-V nitride semiconductor material, which has recently received increased attention owing to its many potential applications. The majority growth technique for InN growth is the molecular-beam epitaxy (MBE), due to its ability to produce active nitrogen growth species using plasma, essential for low temperature (~500 °C) growth. The other frequently used InN growth method is metalorganic chemical vapor deposition (MOCVD) which has proven significantly more challenging due to the high thermal stability of NH3 ? a typically used source of nitrogen. However, there is a significant interest in developing of the MOCVD process for the epitaxial growth of InN compatible with commercial growth of other group III-nitride thin films. Unfortunately, when sapphire substrate is used for InN growth, difficulties arise due to large lattice mismatch (?25.7%) and coefficient of thermal expansion (CTE) difference (? -48.5%) between them. However, the lattice mismatch and CTE difference (?10% and ?-31%, respectively) between InN and GaN is also high. The unintentional n-type conductivity of InN with high free-electron concentrations (1021cm?3) is typically considered to be caused by (i) donor impurities, e.g. oxygen or hydrogen, and (ii) donor-type native defects, e.g. nitrogen vacancy VN also confined in the core of edge-type threading dislocations (TDs). To reduce the number of TDs the InN layer were grown on the 340nm-thick InAlN buffer layer deposited at 709 °C and chamber pressure of 200 mBar with 0.67 In molar fraction ? lattice mismatch to InN (4.2%). The InN/InAlN structures were grown by MOCVD on on- and off-axis c-plane (0001) Al2O3 substrates. Off-axis substrates were misoriented toward the m- or a-plane by 4°. The 20nm thin InN layers prepared on off-axis substrates were grown at 800 mBar and either 600°C (4° misorientation toward m- and a-plane, referred to as 600m and 600a), or at 550°C (misorientation toward a-plane, referred to as 550a). The electrical properties of the nominally undoped thin InN films were analyzed by temperature-dependent Hall-effect measurements and correlated to the structural defects evaluated by the X-ray diffraction (XRD). Obtained results can be summarized as follows: i) electron mobility monotonically decreased with the increase in the density of edge-type TDs in the samples; ii) a relatively weak temperature dependence of the electron mobility in the low temperature region (up to 100K) suggests dislocation scattering was dominant; iii) the higher temperature dependence of electron mobility were observed in the moderate temperature region (up to 300K), which corresponds to acoustic-phonon (AP) scattering via piezoelectric scattering; iv) the lowest electron mobility of the structure growth on off-axis c-plane substrate can be explained higher RMS roughness (2.2nm) compare with the structure growth on on-axis c-plane substrate (1.3nm).

Authors : Thomas O’Connor1,2*, Vitaly Zubialevich1 Stefan Schulz1,3 & Peter Parbrook1,2
Affiliations : 1Tyndall National Institute, University College Cork, Cork, Ireland 2School of Engineering, University College Cork, Cork, Ireland 3Department of Physics, University College Cork, Cork, Ireland

Resume : As the emission wavelength of III-Nitride materials reduce, and delve deeper into the UV region, the struggle to keep the material at a high internal quantum efficiency escalates. A reduction in the quantum confined Stark effect and an improvement in strain engineering are just two of the challenges that wurtzite boron nitride (wz-BN) could play a key role in. This is due to the many unique parameters that wz-BN exhibits, such as a small lattice constant [1] and dissimilar piezoelectric coefficients [2] when compared to the conventional wurtzite III-N materials (InN, GaN, AlN). In this presentation, we investigate the possibility of incorporating wz-BN into GaN/AlGaN multiple quantum wells (MQW) serving as the active region for UV emitters. To our knowledge, this is the first report of a ternary MQW containing wz-BN grown on a sapphire substrate by MOCVD. MQWs of BGaN with an AlGaN barrier were grown by MOCVD in a 3x2” showerhead-type AIXTRON reactor using trimethylgallium (TMGa), trimethylaluminium (TMAl) and triethylboron (TEB) as group III precursors and ammonia (NH3) as a source of nitrogen. Nitrogen was used as the main carrier gas. The vapour phase B/III ratio was varied to identify the impact on the boron incorporation. The active region was grown on top of a 200 nm AlN connecting layer and an AlGaN buffer layer. The substrate used was a c-plane AlN/sapphire template (Kyma Technologies). X-ray diffraction (XRD) was used to determine the structural properties of the material, in particular the impact BN had on the MQWs. This was achieved by measuring ω-2θ scans, using symmetric (002) reflections. For low amounts of BN incorporation, rather sharp and smooth interfaces within the MQW stack were observed. Roughening at the interfaces increased between the quantum wells and barriers with a TEB/III ratio of 3%. This was seen by the smearing out of the MQW-related features in the XRD curves. The emission spectra from the MQWs was also observed at low and room temperature by photoluminescence measurements using a continuous-wave Ar+ ion 244 nm laser as the excitation source. A 3 nm redshift in the emission wavelength and an increase in intensity was observed with the introduction of low amounts of boron, this was then followed by a reduction in intensity and a further redshift by 13 nm relative to the reference sample for the sample containing the highest TEB/III ratio. The observed redshift may stem from a large bandgap bowing parameter, which can be seen for ternary III-N compounds containing BN [1,3]. From literature the growth of thin layers resulted in the observation of columnar growth[4]. This correlates with the roughening observed by XRD with increasing BN incorporation. This work was funded by Science Foundation Ireland (IPIC and PIADs.) [1] M.E. Turiansky et al. J. Appl. Phys 126, 095706 (2019) [2] C.E. Dreyer et al. Appl. Phys. Express, 7, 031001 (2014) [3] J.X. Shen et al. Phys. Rev. Materials 1, 065001 (2017) [4] S. Gautier et al. J. Cryst. Growth, 315, 288 (2011)

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Session 2 - Structure, stress and defects in epitaxial materials-2 : E. M. Alkoy
Authors : M. Bouabdellaoui(a), L. Favre(a), M. Bollani(b), Olivier Gourhant(c), Fabien Deprat(c), Christophe Duluard(c), Anne-Flore Mallet(a,c), E. Assaf(a), A. Ronda(a), M. Abbarchi(a), I. Berbezier(a)
Affiliations : aCNRS, IM2NP, Aix-Marseille University, Faculté des Sciences de Saint-Jérôme, case 142, 13397 Marseille, France b Institute of Photonic and Nanotechnology - Consiglio Nazionale delle Ricerche (IFN-CNR), L-NESS, via Anzani 42, Como, Italy c Digital Front End Manufacturing & Technology STMicroelectronics Crolles, France

Resume : The silicon photonic platform is the mainstream technology used currently, due to its scalability up to 12inch wafers and wafer-scale co-integration with high-speed electronics using existing techniques. It is intensively investigated for keeping on track with Moore's Law, by using optical interconnects to provide faster data transfer both between and within microchips. But its interest goes far beyond optical communications at the 1.55µm wavelength used by fiber optic telecommunication systems. In particular, for applications such as 3D imaging or facial recognition, it becomes necessary for the sensor to operate in the near infrared (NIR) wavelength range, particularly at 940nm. CMOS image sensors on silicon substrate absorb the light in the photodiode area but they need to be deep (typically 1 to 10 µm) to absorb the maximum amount of light (especially at long wavelengths) and free of defects, since each defect acts as a center of recombination of the electron-hole pairs formed during the light absorption. By contrast, germanium photodiodes, which are available on the major silicon photonics platforms, typically show a much higher quantum efficiency with an absorption coefficient almost two decades higher than silicon at 940nm. However, the main bottleneck is the fabrication of monocrystalline thick Ge layers on Silicon On Insulator (SOI) substrate, that cannot be fabricated by direct epitaxy. In this presentation, we will review the various fabrication processes developed for the fabrication of GeOI systems. We will also discuss a new fabrication process based on the combination of epitaxy and condensation. We show that different strain relaxation regimes can be distinguished. While before the total oxidation of the underlying SOI layer, the SiGe/SOI samples remain perfectly strained without elastic relaxation, the first stages of relaxation start at concentrations x ? 0.5, where partial and local relaxation were revealed by High Resolution Transmission Electron Microscopy (HRTEM) observations. At this stage, relaxation proceeds through the slow diffusion and motion of matter at the Si1-xGex/SiO2 interface. Large variations of strain distribution on different areas along the interface was quantitatively assessed by Geometric Phase Analysis (GPA). The mechanism results in the morphological evolution and local swelling of the SiGe embedded layer, facilitated by the viscous ?ow of SiO2. GPA confirms that the lateral expansion leads to the relaxation of the strain accumulated during condensation of Ge. This demonstrates that even at low temperature, SiO2 can serve as an efficient compliant substrate for strain engineering of defect-free Ge rich Si1-xGex thin films. At higher Ge concentration, typically for pure Ge, full relaxation is obtained by an original buckling instability phenomenon, which results in a large periodic undulation. To prevent this undulation, periodic patterns are performed by e-beam lithography in the top SiGe epitaxial layer before oxidation. In the areas that do not contain any pattern, TEM cross-section observations show either local undulations of the Ge-rich films or large density of dislocations. However, in the patterned areas, the TEM /GPA analyses show that for optimized patterns periodicity and geometries, a fully relaxed defect-free ultrathin Ge layer can be obtained. The last fabrication step of Ge photodiode which consists of the re-epitaxy of a thick and relaxed Ge layer to maximize the photon absorption is under progress.

Authors : (a) Matthew Zervos ; (b) Andreas Othonos
Affiliations : (a) Nanostructured Materials and Devices Laboratory, School of Engineering, University of Cyprus, PO Box 20537, Nicosia, 1678, Cyprus. (b) Laboratory of Ultrafast Science, Department of Physics, University of Cyprus, PO Box 20537, Nicosia, 1678, Cyprus.

Resume : Cu3N is a novel semiconductor in which crystal imperfections such as Cu interstitials and nitrogen vacancies give rise to states that are energetically located inside or very close to the conduction and valence bands respectively but do not give rise to any mid gap states. Consequently, it has been suggested to be a defect tolerant semiconductor that could be attractive as as a solar cell absorber in view of the fact that it has an indirect energy band gap of 1.0 eV but also due to the fact that n- and p-type doping are possible. In addition, Cu3N has been used successfully for energy storage as it can act as a host for Li ions in batteries. Here it is shown that Cu3N can be grown on Al2O3 by halide vapor phase epitaxy in a two-step process using CuCl2 under an excess of 800 ml min-1 NH3 at 600 °C which leads to the deposition of Cu that is subsequently converted into Cu3N under NH3:O2. The reaction of CuCl2 in CH3CH2OH with an excess of NH3 did not lead to the direct growth of Cu3N which is different to the case of halide vapor phase epitaxy of III-V semiconductors. The Cu3N layers obtained in this way have an anti-ReO3 cubic crystal structure and we have clearly observed the M- and R-direct energy band gaps by ultrafast pump-probe spectroscopy in excellent agreement with density functional theory calculations of the electronic structure. We also find that the reaction of CuCl2 under a smaller flow of NH3 will lead to the deposition of cubic Cu2O which is an active topic of investigation due to the observation of giant Rydberg excitons by Kazimierczuk et al. [1] who confirmed the existence of Rydberg excitons with principal quantum numbers as large as n = 25 and giant wavefunction extensions. More recently Rydberg exciton?polaritons were observed in a Cu2O microcavity [2] but all of the above ground-breaking discoveries were observed in naturally occurring Cu2O crystals which has instigated the need for the epitaxial growth of high crystal quality Cu2O. The Cu2O films obtained here have a cubic crystal structure and display a detailed spectral structure by ultrafast pump probe spectroscopy that has not been previously observed. This is currently the main focus of attention along with ongoing investigations into the growth of Cu2O on lattice matched layers other than Al2O3. [1] T. Kazimierczuk, D. Fröhlich, S. Scheel, H. Stolz, M. Bayer, Giant Rydberg Excitons in the Copper Oxide Cu2O, Nature, (2014), 514, 343. [2] Konstantinos Orfanakis, Sai Kiran Rajendran?, Valentin Walther?, Thomas Volz, Thomas Pohl and Hamid Ohadi, Nature Materials, 2022.

Authors : E. Scalise{1}, F. Glas{3}, M.A. Verheijen{4,5}, E.P.A.M. Bakkers{4}, A. Marzegalli{1,2}, L. Miglio{1}
Affiliations : 1-L-NESS and Department of Material Science, Università degli Studi di Milano-Bicocca, via R. Cozzi 55, I-20125 Milano, Italy; 2-Department of Physics, Politecnico di Milano, via Anzani 42, I-22100 Como, Italy; 3-Centre de Nanosciences et de Nanotechnologies / Centre for Nanoscience and Nanotechnology (C2N) CNRS, Université Paris-Saclay, 10 boulevard Thomas Gobert, 91120 Palaiseau, France; 4-Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands; 5-Eurofins Materials Science Netherlands BV,5656 AE Eindhoven, The Netherlands

Resume : The hexagonal crystal phase of Ge (2H-Ge) is a metastable and extremely promising form, due to the direct bandgap that allows for efficient light emission, particularly in the Ge-rich SiGe alloy. Its synthesis has recently become an important challenge for researchers. Fadaly et al. [1] obtained photoemission from 2H-Ge and 2H-SiGe epitaxial shells, grown around almost lattice-matched wurtzite GaAs nanowire cores. The structural quality of these materials, essential for such applications, has been discussed in Fadaly et al. [2]. There, we identified a specific planar defect, having a triangular shape in the nanowire cross-section, being the I3 basal stacking fault and confined within partial dislocations. The detailed atomistic structure of this complex has been revealed and the harmless electronic nature for emission (no gap states) has been predicted by first principle calculations, and experimentally confirmed. Here, we go further in the defect analysis, modelling possible intrinsic formation mechanisms during the shell growth. In fact, it appears that the defect may originate at any point in the growth front of the shell, independently of the similar ones stemming from the GaAs interface. We propose the key atomistic process leading to the nucleation of the defect triangular apex, considering the growth-front and the dislocation reconstructions, by first principle calculations. An alternative evolution to the original fault is also proposed, possibly leading to a simple point defect. The latter is not easily observed via direct TEM imaging of the nanowires, so we still do not have evidence of its occurrence, in parallel to the extended I3 defects. Therefore, possible initial stages of the two defects just after the fault nucleation have been investigated via first principles calculations, allowing us to argue the stability of the subsequent growth steps. Finally, by considering the structural complex embedding the point defect, we propose a bonding reconstruction and calculate the relative electronic properties, which might constitute an alternative spectroscopic way of assessing whether it appears, or not. [1] E.M.T. Fadaly et al., Direct-Bandgap Emission from Hexagonal Ge and SiGe Alloys, Nature 2020, 580 (7802), 205?209. [2] E.M.T. Fadaly et al., Unveiling Planar Defects in Hexagonal Group IV Materials, NanoLett. 2021, 21, 3619?3625.

Authors : Yedra, L., Blanco-Portals, J. , López-Conesa, L., Martín, G., Ruiz-Caridad, A., Baiutti, F.4, Chiabrera, F., Diercks, D., Cavallaro, A., Garbayo, I., Walls, M., Lippert, T., Pergolesi, D., Niania, M., Ruiz-González, L., Kordatos, A., Núñez, M., Morata, A., Chroneos, A., Aguadero, A., Kilner, J., Tarancón, A., Estradé, S., Peiró, F.
Affiliations : Yedra, L.1,2; Blanco-Portals, J. 1,2; López-Conesa, L. 1,2,3; Martín, G. 1,2; Ruiz-Caridad, A. 1,2; Baiutti, F.4,5; Chiabrera, F.4,6; Diercks, D. 7; Cavallaro, A.8; Garbayo, I.4; Walls, M.9; Lippert, T. 10; Pergolesi, D. 10; Niania, M.8; Ruiz-González, L.11; Kordatos, A.12; Núñez, M.4; Morata, A. 4; Chroneos, A.8,12; Aguadero, A.8; Kilner, J.8; Tarancón, A.4,13; Estradé, S. 1,2; Peiró, F. 1,2 1 Univ Barcelona, Lab Electron Nanoscopies LENS, Micronanotechnol & Nanoscopies Electrophoton Devi, Dept Elect & Biomed Engn, C Marti & Franques 1, Barcelona 08028, Spain 2 Univ Barcelona, Inst Nanosci & Nanotechnol IN2UB, C Marti & Franques 1, Barcelona 08028, Spain 3 Univ Barcelona CCiTUB, TEM MAT Unit, Sci & Technol Ctr, C Lluis Sole & Sabaris 1, Barcelona 08028, Spain 4 Catalonia Inst Energy Res IREC, Dept Adv Mat Energy, St Adria De Besos 08930, Barcelona, Spain 5 Natl Inst Chem, Dept Mat Chem, Hajdrihova 19, SI-1000 Ljubljana, Slovenia 6 Tech Univ Denmark, Dept Energy Convers & Storage, Funct Oxides Grp, Fysikvej 310, DK-2332800 Lyngby, Denmark 7 Colorado Sch Mines, Dept Met & Mat Engn, Golden, CO 80401 USA 8 Imperial Coll London, Dept Mat, Prince Consort Rd, London SW7 2BP, England 9 Univ Paris Saclay, Univ Paris Sud, CNRS, Lab Phys Solides, Bldg 510, F-91405 Orsay, France 10 Paul Scherrer Institute, Forschungsstrasse 111 5232 Villigen, Switzerland 11 Univ Complutense Madrid, Dept Quim Inorgan, Fac CC Quim, E-28040 Madrid, Spain 12 Coventry Univ, Fac Engn Environm & Comp, Priory St, Coventry CV1 5FB, W Midlands, England 13 ICREA, Passeig Lluis Co 23, Barcelona 08010, Spain

Resume : Tuning oxygen mass transport properties at the nanoscale offers a promising approach for developing high performing energy materials. Several strategies for engineering interfaces with enhanced oxygen diffusivity and surface exchange have been proposed. However, the origin and the magnitude of such local effects remain largely undisclosed to date due to the lack of direct measurement tools with sufficient resolution. One potential candidate to retrieve the hidden information is the Transmission Electron Microscope (TEM), a powerful instrument that allows the local observation of structures with sub Å resolution. Furthermore, when talking about TEM, it is important to note that a plethora of techniques based on the same instrument have emerged, both in hardware and data treatment software, beyond the conventional observation methods. Atomic resolution in both structural and analytical images is commonplace, and the ever-increasing size of the latter has been the driving force behind the application of big data algorithms to segment and extract the relevant information from spectra [1,2]. Here we focus on a series of materials with mixed electronic and ionic conduction properties (LaxSr1-xMO3 with X = Mn, Cr and (Co,Fe)) where crystalline defects have been determined as the most efficient conduction pathways. Here we show that the adequate characterization of these defects in terms of local order, strain and stoichiometry is an unavoidable step in the understanding of their functional properties. Supported by Atom Probe Tomography results [3], in this work we present the capabilities of several TEM related techniques, High Resolution TEM and Scanning TEM with Geometric Phase Analysis, Energy-Dispersive X-Ray Spectroscopy and Electron Energy-Loss Spectroscopy (combined with clustering methods), to unveil the local phenomena at the atomic scale that ultimately govern the macroscopic properties of electrochemical devices, thus illuminating the path for charge transport engineering in epitaxially grown thin layers. [1] Blanco-Portals, J., Peiró, F., & Estradé, S. (2022). Microscopy and Microanalysis, 28(1), 109-122. [2] Blanco-Portals, J., et. al. (2022). Ultramicroscopy, 232, 113403. [3] Baiutti, F., et al. . (2021). Advanced Materials, 33(48), 2105622.

Authors : Janusz Sadowski, Jarosław Z. Domagała,Wiktoria Zajkowska, Sławomir Kret, Bartłomiej Seredynski, Marta Gryglas-Borysiewicz, Zuzanna Ogorzalek, Rafał Bożek, Wojciech Pacuski
Affiliations : Janusz Sadowski, Institute of Physics Polish Academy of Sciences, Warsaw, Poland Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland, Department of Physics and Electrical Engineering, Linnaeus University, Kalmar, Sweden; Jarosław Z. Domagała, Institute of Physics Polish Academy of Sciences, Warsaw, Poland; Wiktoria Zajkowska, Institute of Physics Polish Academy of Sciences, Warsaw, Poland; Sławomir Kret, Institute of Physics Polish Academy of Sciences, Warsaw, Poland; Bartłomiej Seredynski, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland; Marta Gryglas-Borysiewicz, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland; Zuzanna Ogorzalek, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland; Rafał Bożek, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland; Wojciech Pacuski, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland

Resume : Tantalum arsenide belongs to topological Weyl semimetals (WSM), with unusual electronic and magnetotransport properties. In WSM materials, the combination of distinct features of electronic structure and crystal lattice symmetry (either time reversal or inversion symmetry, but not coincidence of both) leads to occurrence of so called Weyl nodes at the crossing points of two bands without spin degeneracy. The low energy excitations at the Weyl nodes behave as masless Weyl fermions with linear dispersion relations and opposite chiralities. In the band structure of TaAs 12 pairs of Weyl nodes have been identified in the distinct points of the Brillouin zone; but so far TaAs has been obtained only in the form of bulk crystals. We have grown TaAs by molecular beam epitaxy (MBE) on commonly used GaAs(001) substrates, in a III-V MBE system equipped with a valved cracker source for arsenic and e-beam source for Ta. TaAs crystallizes in a body-centred-tetragonal structure with the lattice parameters: a = b = 3.4348 Å; c = 11.641. Using in-situ reflection high energy electron diffraction (RHEED) we observe that in spite of a significant lattice mismatch to GaAs, TaAs grows on GaAs(001) in a fully 2-dimensional layer-by-layer mode, from the very first deposition stage, with no initial 3-dimensional growth typical for epitaxy on the substrates with a high lattice mismatch. The orientation of TaAs is the same as that of the substrate, i.e. TaAs(001) planes are parallel to GaAs(001), but they are rotated by 45 degrees, hence the [110] in-plane direction of the GaAs substrate is parallel to the [010] one of TaAs. Such configuration decreases the lattice mismatch between TaAs and GaAs, but still it is as big as 19%. The twisting of TaAs(001) layers with respect to GaAs(001) substrate is observed in RHEED, and confirmed by X-ray diffraction and transmission electron microscopy (TEM) measurements. Even though no misfit dislocations are identified in TEM cross-sections visualizing the TaAs/GaAs interface, the TaAs surface morphology revealed by atomic force microscopy exhibits stripe-like structure with about 200 nm long and 20 nm thick planar columnar features parallel to GaAs[-110]. This hampers (so far) applicability of angle resolved photoemission spectroscopy (ARPES) to reveal topological properties typical to Weyl semimetals, such as bulk Dirac cones and surface Fermi arcs, due to much larger dimensions of UV-beam spot used in ARPES, but should not be an obstacle in much more local scanning tunneling spectroscopy measurements (to be done). The possibility of obtaining epitaxial layers of TaAs opens a way for integrating this WSM in heterostructures with other materials e.g. ferromagnets or superconductors, which enables investigations of proximity effects, impossible to explore using bulk TaAs crystals accessible so far. This work has been supported by the National Science Centre (Poland), through the project No. 2017/27/B/ST5/02284.

10:30 Coffee Break    
Session 3 - Epitaxy of low-dimensional materials: substrate/epilayer interactions, nanostructures-1 : F. Cheynis
Authors : F. Bonell1, C. Vergnaud1, A. Marty1, H. Boukari2, I. de Moraes1, Q. Guillet1, K. Abdukayumov1, M. Ribeiro1, J. Courtin1, M. Husein1, D. Dosenovic3, H. Okuno3, M. Jamet1
Affiliations : 1: Université Grenoble Alpes, CEA, CNRS, IRIG-Spintec, 17 avenue des Martyrs, 38054 Grenoble, France 2: Institut Néel, Université Grenoble Alpes, CNRS, 25 avenue des Martyrs, 38042 Grenoble, France 3: Université Grenoble Alpes, CEA, IRIG-MEM, 17 avenue des Martyrs, 38054 Grenoble, France

Resume : Transition metal dichalcogenides (TMDs) constitute a class of quantum materials that have gathered a tremendous interest from the solid-state physics community focusing on two-dimensional (2D) materials. They hold promises for numerous applications in photonics and electronics owing to their large exciton binding energies and a transition from an indirect to a direct band gap in the monolayer limit . They also exhibit a strong spin-orbit coupling which is promising for spintronic applications . Until recently, most studies on TMDs have been performed on micrometer-sized flakes mechanically exfoliated from bulk samples . Extensive efforts are beginning to enable the growth of wafer-scale TMD single-crystal films . The absence of lattice matched substrates and the high reactivity of chalcogen atoms prevent the epitaxial growth of monolayers using molecular beam epitaxy (MBE) on usual substrates (Si, Ge, GaAs…). In this presentation, I will discuss our strategy to achieve the growth of single crystalline TMD monolayers by vdW epitaxy . In this regime, the substrate exhibit a van der Waals surface like graphene, mica or Se-passivated GaAs to limit the substrate-epilayer interaction. In a second part, I will present the vdW epitaxy of two TMDs with high spin-orbit coupling on graphene: PtSe2 for the study of spin-charge interconversion phenomena and WSe2 for the study of the valley Nernst effect . Finally, I will demonstrate the clear advantages of MBE and vdW epitaxy to grow well-controlled 2D ferromagnets: Fe5GeTe2 with high Curie temperature close to room and Cr1+dTe2 with tunable magnetic properties by proximity effects and adjusting the stoichiometry d.

Authors : Veniero Lenzi (1,2), José P. B. Silva (1,2), Luís Marques (1,2)
Affiliations : 1: Physics center of Minho and Porto Universities, Campus de Gualtar, 4710-057 Braga, Portugal. 2: Laboratory of Physics for Materials and Emergent Technologies, LapMET, University of Minho, 4710-057 Braga, Portugal.

Resume : Ferroelectric (FE) binary oxides such as Hafnia and Zirconia are key materials for the development of advanced devices, such as non-volatile memories, neuromorphic computing units and supercapacitors. Very recently, ferroelectricity was observed in ultrathin ZrO2 films grown on Si with a thickness of only 5 Å (Cheema, S. et al., Science, 376(6593), 648-652, 2022). However, ZrO2 ferroelectric films are much less studied than HfO2-based ones. In this work, we will show the impact of the Nb:SrTiO3 (STO) substrate orientation on the stability and ferroelectric properties of ZrO2 films grown by ion-beam sputtering. In particular, we will show how orthorhombic phase pure films with negative piezoelectric coefficient d33 could be grown on (011)-oriented substrates, through domain matching epitaxy, while the films grown on (001)- oriented substrates show a mixture of monoclinic and orthorhombic phases. In addition, the role of oxygen vacancies on the stability and ferroelectric properties of epitaxially grown rhombohedral ZrO2 films on (111)-oriented Nb:STO will be also highlighted.

Authors : Maja Remškar, Janez Jelenc, Srečko D. Škapin and Zvonko Jagličič
Affiliations : Jozef Stefan Institute, Solid State Physics Department, Jamova 39, 1000 Ljubljana, Slovenia Institute for Physics, Mathematics and Mechanics, Jamova 39, 1000 Ljubljana, Slovenia

Resume : Superconductive compound Mo6S6I2 belongs to cluster compounds composed of Mo6X8 units (X=S, Se, Te), where part of chalcogen atoms are replaced by iodine as monovalent substituents [1]. In contrary with many other so-called Chevrel phases with the general formula Mo6S8-xIx, which are of needle-like morphology and differ in the site occupation by sulphur and iodine, like Mo6S2I8 [2] and Mo6S4I6 [3], the Mo6S6I2 compound shows a low degree of morphological anisotropy and crystallizes in three-dimensional semi-cubic shape [4]. It’s structure is describes as the hexagonal rhombohedral structure of the PbMo6S8 type with the lattice parameters: aR=6.563 Ǻ and αR=94.5 Ǻ. The critical temperature (Tc) for the superconducting transition in Mo6S6I2 is 14 K. We report on the first quasi-2-dimensional Mo-S-I compound, which nucleates and grows epitaxially on the surface of Mo6S6I2 crystals in shape of thin and rigid belts. Separated from the Mo6S6I2 surface, they are prone to a cleavage along their length, but they keep their growth as thin lamellas. Building units are similar to constituents of quasi one-dimensional Mo6S2I8. The preliminary structural characterization by high-resolution electron microscopy, Raman spectroscopy and magnetic susceptibility measurements have shown that this completely new compound develops a superconductivity at low temperatures with the Tc≈ 4K. Scanning tunnelling spectroscopy (STS) revealed also a huge energy gap of around 8,5 eV. The compound is stable at normal conditions and might be usable for energy storage material. Results of structural characterization of this new Mo-S-I compound in comparison with the Mo6S6I2 cubes and Mo6S2I8 nanowires will be presented and the growth mechanism will be discussed in a model of epitaxy. [1] A. Perrin, C. Perrin and M. Sergent, “Octahedral clusters in molybdenum(II) and rhenium(III) chalcohalide chemistry”, J.Less-Common Metals 137 (1988) 241. [2] C. Perrin, M. Sergent, “A new family of monodimensional compounds with octa-hedral molybdenum clusters. Mo6X8Y2 (X=halogen, Y=chalcogen)”, J. Chem. Res. (S) 2 (1983) 38. [3] M. Remskar, A. Mrzel, M. Virsek, M. Godec, M., Krause, A. Kolitsch, A. Singh, A. Seabaugh, “The MoS2 Nanotubes with Defect-Controlled Electric Properties”, Nanoscale Res Lett 6:26 (2011). [4] M. Sergent, Ø.Fisher, M. Decroux, C. Perrin, R. Chevrel, “Stabilization of Mo6S8 by halogens; new superconducting compounds: Mo6S6Br2, Mo6S6I2, J. of Solid State Chem. 22 (1977) 87.

Authors : P. Baranowski, M. Szymura, R. Georgiev, S. Chusnutdinow, G. Karczewski, T. Wojtowicz, P. Wojnar
Affiliations : P. Baranowski- Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland; M. Szymura- Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland R. Georgiev- Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland S. Chusnutdinow- Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland G. Karczewski- Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland; T. Wojtowicz - International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland; P. Wojnar - Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland;

Resume : A recent observation of excitonic Aharonov-Bohm effect in core/shell nanowires has opened an exciting opportunity to study coherently rotating states in these structures [1], which could be, subsequently, applied in the field of quantum information storage. An important task for the observation of these states is the separation of electron-hole wavefunctions within a nanowire. In ref [1], it has been achieved on GaAs crystal phase quantum dots, which are characterized by a type II band alignment. In this work, an alternative approach for fabrication of quantum dots with type II band alignment inside a nanowire built of II-VI semiconductors is presented. The nanowire heterostructures are grown by molecular beam epitaxy by applying the vapor-liquid-solid growth mechanism assisted with gold catalysts. In the first step, ZnTe short axial insertion inside (Zn,Mg)Te nanowire is fabricated by turning off Mg-flux for a few seconds during the (Zn,Mg)Te nanowire growth. Since ZnTe has a smaller bandgap than (Zn,Mg)Te, a sufficiently short insertion can be considered as a quantum dot inside a nanowire. Subsequently, a few monolayers thick ZnSe shell is deposited around the entire nanowire. ZnTe/ZnSe heterostructure is well-known for the type II character, where electrons tend to localize in ZnSe and holes in ZnTe region. In the last step, the nanowires are coated in a (Zn,Mg)Te passivation shell with the thickness of about 20 nm in order to reduce the impact of surface states on the optical emission. Optimization procedure of the above mentioned structure has been performed. In particular, the several parameters, such as: the length of ZnTe axial insertion, the thickness of the ZnSe shell and Mg concentration inside (Zn,Mg)Te are adjusted. Our goal has been to observe an optical emission from ZnTe/ZnSe nanowire quantum dot. In the case of a ZnTe/ZnMgTe reference structure without ZnSe shell, one observes clearly two distinct optical emission lines coming either from the nanowire (Zn,Mg)Te cores or from the ZnTe quantum dot. The addition of only one monolayer thick ZnSe shell significantly changes the optical emission spectrum. The emission energy of the quantum dot emission shifts significantly from 2.38 eV to 2.00 eV. Simultaneously, its intensity drops by about two orders of magnitude and the decays times increase by the factor of about 10. These observations are consistent with the type I to type II band alignment transition resulting from the presence of ZnSe shell. In μ-photoluminescence the broad emission at 2.00 eV splits into several relatively lines coming from individual nanowire quantum dots. This association is confirmed by the appearance of multiexcitonic emission lines when increasing the excitation power. [1] Corfdir P, et al. Adv. Mater. 31 1805645 (2019)

Authors : K. E. Polczynska, T. Kazimierczuk, P. Kossacki and W. Pacuski
Affiliations : Faculty of Physics, University of Warsaw, Pasteura 5, Warsaw, Poland

Resume : The application of quantum technologies such as spintronics, solotronics, or quantum computing is highly promising when it comes to miniaturization in modern technology. In order to achieve effective devices, there is a need to investigate the spin properties of im- purity interacting with the semiconductor lattice and con ned carriers. Zero-dimensional semiconductor structure such as epitaxial quantum dot (QD) is a model system to probe fundamental interactions in condensed matter. For example, QDs can be used to examine the spin of a single magnetic ion [1,2,3]. Vanadium is a transitional metal with a nuclear spin of 7/2 and 3 electrons on the d shell. It exhibits spin 3/2 in V2+ con figuration [4] leading to two possible fundamental states with spin projection +/- 3/2 or +/- 1/2. Particular spin con figuration is expected to depend on the strain of the crystal lattice in a QD. In this work we examine self-assembled CdTe QDs doped with V, in ZnTe barrier, fabricated using molecular beam epitaxy. We observed a single QD including a single vanadium dopant and measured the magneto-optical properties of such a system. According to numerical modeling based on experimental data, we conclude that V in this case exhibits spin 1/2, which makes our system a realization of a qubit. [1] L. Besombes et al, Phys. Rev. Lett 93, 207403 (2004). [2] J. Kobak et al, Nature Communications 5, 3191 (2014). [3] T. Smolenski et al, Nature Communications 7, 10484 (2016). [4] M. Herbich et al, Phys. Rev. B 59, 2726 (1999).

12:30 Lunch Break    
Session 3 - Epitaxy of low-dimensional materials: substrate/epilayer interactions, nanostructures-2 : M. Jamet
Authors : Joao Marcelo J. Lopes
Affiliations : Paul-Drude-Institut für Festkoerperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Germany

Resume : Two-dimensional (2D) magnetic materials and heterostructures garnered significant attention as they are an ideal platform for exploring exotic physical phenomena such as topological spin configurations. Moreover, they are considered to be promising building blocks for the realization of ultra-compact and novel spintronic devices. A crucial aspect in the development of such 2D crystals for applications is their reproducible and large-scale fabrication. In this talk, I will show recent results on van der Waals (vdW) epitaxy of the 2D ferromagnetic metal Fe5-xGeTe2 (FGT, with 0 ≤ x ≤ 2) on graphene and hexagonal boron nitride templates. In this context, the employment of defect engineering to exert control over nucleation during vdW growth will also be discussed. FGT film synthesis was performed via molecular beam epitaxy using elemental Fe, Ge, and Te evaporated from Knudsen cells, and substrate temperatures between 200 and 300 C. Morphological and structural characterization of the heterostructures with various methods show that very good crystalline quality can be achieved. Furthermore, magneto-transport along with magnetometric measurements reveal composition-dependent magnetic anisotropies and Curie temperatures. Importantly, ferromagnetic order with a predominant easy out-of-plane orientation can be stabilized above room temperature by incorporating sufficiently high Fe amounts in the FGT structure. A detailed correlation between the structural evolution and ferromagnetism in the FGT films will be presented. These results are relevant for the further development of wafer-scale fabrication of layered magnetic materials and heterostacks aiming at the realization of multifunctional, atomically thin devices.

Authors : Emmanuel CHEREAU (1,2), Gabin GREGOIRE (1), Geoffrey AVIT (1), Catherine BOUGEROL (3,4), Alain MOREAC (5), Jean-Pierre LANDESMAN (6), Philip SHIELDS (7), Agnès TRASSOUDAINE (1), Evelyne. GIL (1), Ray.R. LAPIERRE (2), Yamina ANDRE (1)
Affiliations : (1) Université Clermont Auvergne, Clermont Auvergne INP, CNRS, Institut Pascal, F-63000 Clermont-Ferrand, France; (2) Department of Engineering Physics, McMaster University, Hamilton, Ontario, Canada, L8S4L7; (3) Univ. Grenoble Alpes, F-38000 Grenoble, France; (4) CNRS, Institut Néel, F-38042 Grenoble, France; (5) Univ Rennes, CNRS, IPR-UMR 6251, F-35000 Rennes, France; (6) Univ Rennes, INSA Rennes, CNRS, Institut FOTON-UMR 6082, F-35000 Rennes, France; (7) Department of Electronic & Electrical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK

Resume : For more than 20 years, III-V semiconductor nanowires (NWs) have been studied to build blocks for future electronic and optoelectronic devices. Nevertheless, making functional NW-based devices is complex, due to the limited capability of current bottom-up and top-down methods to achieve reproducible NWs arrays. VLS growth methods used to obtain high aspect ratio NWs are not a suitable option, since incorporation of catalyst particles in NWs could introduce deep level recombination centers that significantly degrade the electrical and optical properties. Today, the most reliable process to control the growth of well-ordered III-V NWs with high reproducibility is Selective Area Growth (SAG). In this work, we demonstrate the possibility of making III-As NWs arrays by SAG-Hydride Vapour Phase Epitaxy (SAG-HVPE). Perspectives of this work concern multispectral infrared photodetectors for InAs [1] and betavoltaic cells for GaAs [2], which require dense arrays of high aspect ratio NWs. In SAG-HVPE, the chloride precursors provide a suitable environment to implement selective and localized growth since they do not adsorb on the dielectric surface. Moreover, HVPE is a fast growth (up to a few tens of µm/h) cost-effective technique which allows to produce high aspect ratio NWs in limited process time. GaAs NWs growth experiments were carried out on on GaAs (111)B substrates. Systematic studies of the influence of the V/III ratio and growth temperature on the NWs morphology were performed. Doping experiments have been carried out using Si (n-doping) and Zn (p-doping) precursors. Samples were characterized by photoluminescence (PL) and transmission electron microscopy (TEM). GaAs NWs arrays were also grown on Si (111) substrates. The specific conditions required for nucleation and growth of GaAs inside opened Si apertures are described. The temperature is the main factor to control the shape of the NWs: the morphology can be switched from platelets to NWs. TEM analysis showed a perfect zinc blende crystal quality for the platelets. Growth of InAs NWs has also been carried out on GaAs (111)B and Si (111) substrates. Similar to GaAs, the morphology of InAs structures is controlled with different growth parameters. According to COMSOL simulations, the InAs absorptance peak depends on the NWs array design: pitch and diameter of the apertures. Fourier-transform infrared spectroscopy (FTIR) performed at room temperature on InAs NWs grown by SAG-HVPE actually showed a shift of the absorptance peak, from 0.4 eV to 0.8 eV for NWs diameters of 630 nm and 310 nm, respectively [3]. References: [1] R.R. LaPierre et al 2017, J. Phys. D: Appl. Phys. 50 123001. [2] D.L. Wagner, D.R. Novog, and R.R. LaPierre, J. Appl. Phys. 127, 244303 (2020). [3] G. Grégoire, Crystal Growth & Design 2021 21 (9), 5158-5163.

Authors : P. Wojnar 1, J. Plachta 1, T. Kazimierczuk 2, P. Kossacki 2, G.Karczewski 1, T. Wojtowicz 3
Affiliations : 1 Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, PL-02-668 Warsaw, Poland 2 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, PL-02-093 Warsaw, Poland 3 International Research Centre MagTop, Aleja Lotników 32/46, PL-02-668 Warsaw, Poland

Resume : Quantum confinement in semiconductor heterostructures results in the enhancement of excitonic effects leading to numerous applications related, for instance, to the improvement of the room temperature performance of optical devices. Strikingly, between well-studied two-dimensional and zero-dimensional systems lays an underexplored region of one-dimensional quantum wires (QWRs). In this work, the fabrication of ultra-thin (Cd,Mn)Te nanowires with diameters reaching values below 10 nm is reported. The structures are grown in a system for molecular beam epitaxy by employing the vapor-liquid-solid growth mechanism assisted with gold catalysts. The thinning procedure relies on a thermally induced reverse reaction process, which is applied in-situ on nanowires in the same growth process. Subsequently, the nanowire cores are covered with (Cd,Mg)Te passivation shells to activate the excitonic emission. Importantly, it is found, that the optical emission from ultra-thin nanowires exhibits a distinct blueshift as compared to reference nanowires grown in identical conditions but without the annealing step. This is the first strong indication for the influence of the quantum confinement effects in these structures. While the reference nanowires emit light in the relatively narrow spectral range 1.59 eV – 1.62 eV, the emission from thermally thinned nanowires extends from 1.5 eV to 1.75 eV. Moreover, it is found based on cathodoluminescence study that the emitting objects can be significantly shorter than the nanowires themselves. The emitter region length can be correlated with emission energy, while shorter regions emit at higher energy. This result indicates that excitons can be localized at fluctuations of nanowire core diameter. Therefore, not only the radial but also the axial quantum confinement should be, most likely, taken into account while considering the properties of excitonic emission from ultra-thin (Cd,Mn)Te nanowires. The advantage of the use of Mn-containing II-VI semiconductors, such as (Cd,Mn)Te, is the opportunity to determine the light hole - heavy hole splitting values within individual nanowires by employing the presence of the giant Zeeman effects. A detailed magneto-optical reveals that not only the light hole - heavy hole splitting but also the character of the excitonic emission depends on the emission energy. The nanowires emitting at relatively low energy exhibit a light hole character while the excitonic emission has predominantly heavy hole character in nanowires emitting above 1.70 eV. This finding is explained in terms of competition between strain and radial quantum confinement leading to the light hole character of excitons, and localization of excitons in the axial direction which promotes the heavy hole excitons. This research was partially supported by the National Centre of Science (Poland ) through grant 2017/25/N/ST3/00621, and by the Foundation for Polish Science through the IRA Programme co-financed by EU within SG OP (grant No. MAB/2017/1).

Authors : Arnas Pukinskas1, Nerijus Jurkūnas2, Silvija Keraitytė1,3, Algirdas Jasinskas1, Andrea Zelioli1, Simona Pūkienė1, Bronislovas Čechavičius1, Arnas Naujokaitis1, Martynas Skapas1, Monika Jokubauskaitė1,3, Evelina Dudutienė1, and Renata Butkutė1,3
Affiliations : 1 Department of Optoelectronics, Centre for Physical Sciences and Technology, Saulėtekio av. 3, Vilnius, Lithuania 2Optonas Ldt., Savanorių av. 235, Vilnius, Lithuania 3Institute of Photonics and Nanotechnology, Faculty of Physics, Vilnius University, Saulėtekio av. 3, Vilnius, Lithuania

Resume : The AIII-BV-Bi semiconductor, called bismide, is one of the most perspective compounds for the NIR applications because of their unique properties – much faster than of classical semiconductors band gap energy reduction replacing As by Bi atoms and less temperature sensitive Eg. Theoretically it was demonstrated, that 1% of Bi can reduce the band gap energy up to 88 meV. Thus, using GaAs platform and introducing up to 10 % of Bi, the optical features of GaAsBi compound could cover spectral region containing all three telecomunication windows up to1550 nm. Moreover, due to lower band gap energy temperature dependence, bismide alloy based NIR light sources could easily work at room temperature without additional cooling. Despite these advantages their application progress is still hold back by technological challenges: low bismide growth temperature and stoichiometric ratio of Ga and As fluxes used to introduce higher bismuth concentration. The difficulties to insert larger content than 6% Bi due to much larger than As bismuth radius, and tendency to surface segregation, consequently Bi droplets of several hundred nanometers size formation, is one more factor insisting to find the new concepts for GaAsBi and Bi employment in NIR sources. Bulky Bi known as a semimetall with reduction of dimension lower than 60 nm transforms to indirect semiconductor. Further minimization below 16 nm Bi changes from indirect to direct semiconductor, exhibiting 0.7-1.0 eV band gap and extending the application area of GaAsBi and Bi based nanostructures. In this work, bismuth segregation process was explored as an alternative of Bi QDs formation way to usual Stranski-Krastanov method. Bi quantum dots have been formed employing in-situ bismuth segregation process in Molecular Beam Epitaxy (MBE) reactor via annealing of GaAsBi/AlGaAs single or multiple quantum wells (QWs) for a short time at 600-750oC temperatures under arsenic overpressure conditions. The optimization of QWs growth and in-situ annealing conditions was performed to found the crucial technological parameters: quantum barriers composition (which could play Bi blocking layer role as well), GaAsBi well composition (max Bi content) and geometry (well thickness and shape) influencing Bi QD density in the well and its orientation. Featured samples were characterized using high resolution transmission electron microscopy (HR-TEM), meanwhile all grown quantum structures were examined by photoluminescence (PL) measurements.

Authors : Teemu Hakkarainen, Joonas Hilska, Abhiroop Chellu, Mircea Guina
Affiliations : Optoelectronics Research Centre, Physics Unit, Tampere University, Finland

Resume : Solid-state single and entangled photon emitters linked coherently over long distances with optical fibers enable a new generation of quantum-based communications networks. Currently, epitaxial semiconductor quantum dots (QDs) pave the way as a scalable approach for fabricating deterministic non-classical light sources that can be integrated with other photonic or electronic components in miniaturized form. While multiple epitaxial QD fabrication methods exist, arguably the most successful approaches have been based on local droplet etching (LDE) involving materials based on GaAs and AlGaAs.[1] However, this material system is limited to the 680-800 nm wavelength range owing to their direct band gap range, and thus are not suitable for long-haul transmission over optical fibers. In this work, we present a highly analogous but novel LDE-QD system based on GaSb and AlGaSb [1,2], which emit at telecom wavelengths around 1.5 um with room for expansion towards 2 um and beyond. Here, we first describe how the LDE process works in the GaSb/AlGaSb system. The process is initiated by forming metallic nanodroplets over a flat AlGaSb surface by deposition of Al or Ga [1,2]. These nanodroplets are then annealed under a low Sb-flux which triggers an etching process of the underlying AlGaSb material, thus forming a nanohole on the surface. The nanoholes can then be filled by GaSb and subsequently overgrown with AlGaSb, thus forming GaSb QDs embedded in an AlGaSb matrix. We show how this process of nanohole fabrication can be accurately controlled by fine tuning the epitaxial growth parameters, which allows us to control the morphology and density of the resulting QDs. For example, we demonstrate three-orders-of-magnitude tunability in the nanohole density, as well as the different characteristic morphologies of nanoholes etched by Ga and Al. After understanding the growth process, we demonstrate the different emission properties of GaSb LDE-QDs. In ensemble (large area) low temperature photoluminescence measurements, the QDs show ground state emission at 1.48 µm wavelength with an extremely narrow peak width of around ~8 meV, demonstrating excellent uniformity of the QDs. In single-QD micro-photoluminescence measurements, the QD emission is characteristic of single-exciton dominated spectra with very narrow linewidths and linear power scaling. In addition to these promising emission properties, we show an interesting effect whereby tuning the degree of filling of the nanoholes, the QDs undergo a indirect-to-direct bandgap crossover, which would enable a QD system that could be tuned from highly luminescent to a non-luminescent in a controllable way. 1. M. Gurioli, Z. Wang, A. Rastelli, T. Kuroda, S. Sanguinetti, Nature Materials 18, 799 (2019). 2. J. Hilska, A. Chellu, T. Hakkarainen, Cryst. Growth Des. 21 1917−1923, 2021 3. A. Chellu, J. Hilska, J.-P. Penttinen, T. Hakkarainen, APL Materials 9, pp. 051116, 2021

15:30 Coffee Break    
Session 3 - Epitaxy of low-dimensional materials: substrate/epilayer interactions, nanostructures-3 : J. M. Lopes
Authors : Valentina Zannier1, Isha Verma1, Sedighe Salimian1, Stefan Heun1, Francesca Rossi2, Daniele Ercolani1, Fabio Beltram1 and Lucia Sorba1
Affiliations : 1 NEST, Istituto Nanoscienze - CNR and Scuola Normale Superiore, Piazza San Silvestro 12, I-56127 Pisa, Italy 2 IMEM-CNR, Parco Area delle Scienze 37/A, I-43124 Parma, Italy

Resume : Indium antimonide (InSb) has a narrow band gap, high carrier mobility, small effective mass, and is a promising candidate for the implementation of topological superconducting states. Remarkably, the interest in this material has increased in recent years thanks to the possibility to overcome the limitation of its integration with lattice-mismatched substrates in nano-heterostructures. However, the realization of InSb nanostructures with a high crystal quality and a well-controlled morphology is still challenging. In this contribution, we show the growth of free-standing InSb nanostructures on InAs and InP nanowire stems by means of Au-assisted chemical beam epitaxy. We demonstrate that nanowires (1D), nanoflags (2D), and nanocubes (3D) can be obtained by tailoring growth parameters like growth temperature, precursor fluxes, sample rotation, and substrate orientation. Indeed, the InSb shape evolution is a result of the interplay between axial vapor-liquid-solid (VLS) growth, radial vapor-solid (VS) growth, and possibly directional-driven growth. Concerning the nanoflags, through morphological and crystallographic characterization we demonstrate that they are single-crystalline with a defect-free zinc blende structure and stoichiometric composition. The existence of two families of nanoflags, characterized by an aperture angle at the base of 145° and 160°, is observed and modelled [1]. Finally, we have further optimized the size of these free-standing 2D InSb nanoflags. In fact, by employing more robust and tapered NW stems and precisely orienting the substrate with the help of reflection high-energy electron diffraction (RHEED) patterns, we could maximize length and width, and minimize the thickness of the nanoflags [2]. This allowed us to fabricate Hall-bar devices with suitable length-to-width ratio enabling precise electrical characterization of single nanoflags. An electron mobility of ~29,500 cm2/Vs at 4.2 K was measured, which is the highest value reported for free-standing 2D InSb nanostructures in literature. We have also successfully fabricated ballistic Josephson junction devices with 10/150 nm Ti/Nb contacts that show gate-tunable proximity-induced supercurrent (∼ 50 nA at 250 mK) [3]. The devices also show clear signatures of subharmonic gap structures, indicating phase-coherent transport in the junction and a high transparency of the interfaces. Our study provides useful guidelines for the controlled growth of high-quality InSb nanostructures with different shape, and evince the use of 2D InSb nanoflags for fabrication of advanced quantum devices. [1] I. Verma et al., Nanotechnology 31, 384002 (2020). [2] I. Verma et al., ACS Appl. Nano Mater. 4, 5825–5833 (2021). [3] S. Salimian et al., Appl. Phys. Lett. 119, 214004 (2021).

Authors : T. Sodhi1-2, P. Chrétien2, L. Couraud1, L. Travers1, J.C. Harmand1, F. H. Julien1, M. Tchernycheva1, F. Houzé2, N. Gogneau1
Affiliations : 1Centre de Nanosciences et Nanotechnologies, Université Paris-Saclay, CNRS, UMR9001, Palaiseau, France ; 2Laboratoire de Génie électrique et électronique de Paris,Université Paris-Saclay, CentraleSupélec, Sorbonne Université, CNRS, Gif sur Yvette, France

Resume : A new generation of piezoelectric generators based on 1D-nanostructures is appeared, these last years, to develop autonomous power micro-systems. Thanks to their high crystalline quality, their high mechanical properties and their large surface-to-volume, nanowires (NWs) present advantages to significantly enhance the generator conversion efficiency. However, due to their nanoscale dimensions, the nanostructures are also characterized by “new” properties, non-significant at micrometric scales, that can lead to a strong modulation of their characteristics. Among these “new” properties, we can cite the modulation of the free carrier concentration in the NW volume due to the presence of the surface charge (SC) effects, strongly pronounced in sub-100 nm wide GaN NWs. Although these effects are under debate, their potential detrimental (in nanoscale electronic and optoelectronic devices) or advantageous (in nanoscale piezoelectric devices) roles have already been pointed out. In-depth understanding and control of the influence of SC on the NW properties is thus crucial to fully take advantage of these 1D-nanostructures and thus develop high-efficient NW-based devices. Characterization at the nanoscale is challenging, and the development of new nano-characterization techniques is required. Here we investigate the effects of the SC through the characterization of the piezo-conversion properties of GaN NWs, by using a new advanced nano-characterization tool. It is well known that the free carriers degrade the piezoelectric response, due to their screening of the piezoelectric charges. The modulation of their concentration by varying the SC effects thus results in the variation of the piezo-response of NWs. Thanks to two different experimental configurations, we demonstrate the influence of the NW environment as well as of the NW dimensions on the expression of the SC and thus on the piezoelectric conversion properties of GaN NWs. Especially, we establish that the SC effects can be extremely favorable for strongly improving the electromechanical conversion efficiency of GaN NWs.

Authors : Aleksandra K. Dąbrowska, Mateusz Tokarczyk, Grzegorz Kowalski, Johannes Binder, Rafał Bożek, Jakub Iwański, Roman Stępniewski, Andrzej Wysmołek
Affiliations : Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland

Resume : Boron nitride (BN) in the sp2 – hybridized structure is a material with extremal resistance to external conditions, characterized at the same time by a wide band gap (approximately 6 eV) and two-dimensional nature [1]. Such a combination of properties provides a wide range of possible applications, from deep UV light sources, through protective layers and insulating barriers to one of the building blocks in van der Waals heterostructures [2]. Despite the great progress in the growth technologies of the BN layers [3,4], there is no suitable method that would provide high-quality and large area layers, which would scale with the size of the substrate used. In this communication, we present our achievements in the growth of boron nitride by Metal Organic Vapour Phase Epitaxy (MOVPE) – a method that could fulfill the above-mentioned requirements. In this technique, BN is grown on sapphire substrates as a product of the chemical reaction between ammonia (nitrogen precursor) and triethylborane (TEB, boron precursor). The traditional growth modes used in MOVPE are still very limited in obtaining high-quality layers. Our new approach – two-stage epitaxy [5] allows overcoming some of the limitations of previous methods. In this regime, a thin (a few nanometers), preordered layer grown in Continuous Flow Growth mode (CFG) [6] is treated as a buffer for a more effective growth by Flow-rate Modulation Epitaxy [7]. Such a combination allows to avoid chaotic nucleation on the substrate and leads to the formation of boron nitride with a lattice constant very close to those of the best bulk h-BN crystals. Our studies show that achieving boron nitride with properties comparable to those of bulk material but on a large scale by MOVPE may be within reach in the near future [8]. Further tuning of the method and searching for ideal parameters and substrates for growth may allow to transfer the material from research laboratories to practical applications. The advantages and prospects for further development of this novel approach (i.e. influence of the buffer layer, the substrate used, and pregrowth procedures) will be discussed. [1] K.S. Novoselov et al., Science 353, 6298, aac9439 (2016) [2] A.F. Rigosi, et al., J. Phys. Mater. 4, 032003 (2021) [3] K. Zhang et al., J. Mater. Chem. C 5 11992–12022 (2017) [4] A. Pakdel et al., Chem. Soc. Rev. 43 934–59 (2014) [5] A.K. Dabrowska et al., 2D Mater., 8, 015017 (2021) [6] K. Pakuła et al., arXiv 1906.05319 (2019) [7] Y. Kobayashi et al., Journal of Crystal Growth 310, 5048–5052 (2008) [8] K. Ludwiczak et al., ACS Appl. Mater. Interfaces 13, 40, 47904–47911 (2021) Acknowledgment: This work was partially supported by the National Science Centre under grant No. 2019/33/B/ST5/02766

Authors : D. Nazzari*, J. A. Genser*, V. Ritter*, O. Bethge , E. Bertagnolli*, T. Grasser$, W. M. Weber*, A. Lugstein*
Affiliations : * Institute of Solid State Electronics, Technische Universität Wien, Gußhausstraße 25-25a, 1040 Vienna, Austria; Infineon Technologies Austria AG, Siemensstraße 2, 9500 Villach, Austria; $ Institute for Microelectronics, Technische Universität Wien, Gußhausstraße 27-29, 1040 Vienna, Austria;

Resume : Silicene is an attractive candidate for the realization of 2D field effect transistors (2D-FET), owing to its predicted high carrier mobility and bandgap tunability. Its electronic properties can be controlled through an external electric field, perpendicular to the 2D lattice: this requires the deposition of an insulating layer that directly interfaces silicene without perturbing its two-dimensional nature. A promising material is calcium fluoride (CaF2), a crystalline insulator with a high dielectric constant (e=8.43) and wide bandgap (Eg=12.1 eV), known to form a quasi van der Waals interface with 2D materials and with excellent insulating properties even at ultra-thin scales. Its fluorine-terminated surface is chemically inert and free of dangling bonds, strongly reducing the density of traps at the interface. The integration of crystalline CaF2 in MoS2-based FETs has already been successfully shown, yielding high on/off current ratios up to 107 and small hysteresis. A high quality, pinhole-free, single crystal CaF2(111) layer can be grown at relatively low temperatures (250°C) on Si(111) by molecular beam epitaxy (MBE), thanks to the small lattice mismatch (<1%). The obtained material is characterized by an extremely low concentration of defects, allowing layers with a thickness of just 2 nm to be able to withstand high electric fields - up to 27.8 MV/cm - with negligible leakage currents. We demonstrate the epitaxial growth of a thin layer of crystalline CaF2 on 1 monolayer of silicene by MBE. Low energy electron diffraction analysis proves that CaF2 grows epitaxially on all phases of silicene, strictly following the orientation of the 2D lattice underneath. In-situ X-ray photoemission spectroscopy data evidence that, upon CaF2 deposition, no changes in the chemical state of the silicon atoms can be detected, proving that no Si-Ca or Si-F bonds are formed: this clearly shows that the 2D layer is pristinely preserved underneath the insulating layer. The vibrational properties of silicene are analyzed by polarized Raman spectroscopy, evidencing a structural modification of the 2D layer caused by the weak interaction with CaF2. The encapsulated material retains a bidimensional geometry but a clear shift of the vibrational modes hints at an increased buckling and, consequently, at a greater Si-Si bond length. This structural modification could be exploited to open a larger bandgap in silicene. Our work shows that CaF2 and silicene can be successfully interfaced, paving the way for the integration of silicon-based 2D materials in functional devices.

Authors : W. Pacuski1, M. Grzeszczyk1, K. Nogajewski1, A. Bogucki1, K. Oreszczuk1, A. Rodek1, J. Kucharek1, K.E. Połczyńska1, B. Seredyński1, R. Bożek1, K. Ludwiczak1, A. K. Dąbrowska1, J. Binder1, M. Tokarczyk1, J. Iwański1, B. Kurowska2, J. Turczyński2, S. Kret2, T. Taniguchi3, K. Watanabe3, J. Sadowski1,2,4, G. Kowalski1, T. Kazimierczuk1, R. Stępniewski1, A. Wysmołek1, M. Potemski1,5, P. Kossacki1
Affiliations : 1 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura St. 5, 02-093 Warsaw, Poland, 2 Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland 3 National Institute for Materials Science, Tsukuba, 305-0047, Ibaraki, Japan 4 Department of Physics and Electrical Engineering, Linnaeus University, Kalmar, Sweden, 5 Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France

Resume : Monolayer transition metal dichalcogenides (TMDs) are two-dimensional materials with exceptional optical properties such as high oscillator strength, valley-related excitonic physics, efficient photoluminescence, and several narrow excitonic resonances. However, the above effects have been explored so far only for structures produced by techniques involving mechanical exfoliation and encapsulation in hBN, inevitably inducing considerable large-scale inhomogeneity. On the other hand, techniques which are essentially free from this disadvantage, such as molecular beam epitaxy (MBE), have to date yielded only structures characterized by considerable spectral broadening, which hinders most of the interesting optical effects. In this talk, I will present the MBE-grown TMD (MoSe2) exhibiting narrow and fully resolved spectral lines of neutral and charged exciton [1]. Moreover, our monolayers exhibit unprecedented high spatial homogeneity of optical properties, with variation of the exciton energy as small as 0.16 meV over a distance of tens of micrometers. Importantly, good optical properties are achieved for as-grown samples, without any post-growth exfoliation and encapsulation in hBN. Our best recipe for MBE growth includes an extremely slow growth rate, the annealing at very high temperatures, and the use of atomically flat hBN substrate in the form of flakes exfoliated from bulk. Moreover, comparable results are also obtained using an hBN substrate that we grow by MOCVD on 2” Al2O3 wafers [2]. Our optical characterization includes low-temperature PL, PLE, reflectivity, magneto-spectroscopy, time resolved spectroscopy and room-temperature Raman scattering and SHG [1,3]. We compare structural and optical properties of MoSe2 grown on exfoliated hBN to properties of various TMDs (MoTe2 [4,5], NiTe2 [6], WSe2, VSe2) grown on various substrates (2D, 3D, polycrystalline). This reveals particularly high diffusion parameters of transition metals on hBN [5], the role of distribution of orientation of TMD grain domains, the tendency to merge grains or form bilayers and 3D structures. [1] W. Pacuski et al., Nano Letters 20, 3058 (2020). [2] K. Ludwiczak et al., ACS Appl. Mater. Interfaces 13, 47904 (2021). [3] K. Oreszczuk et al., in preparation (2022) . [4] Z. Ogorzałek et al., Nanoscale 12, 16535 (2020). [5] B. Seredyński et al., ArXiv:2111.12433 (2021). [6] B. Seredyński et al., Cryst. Growth Des. 21, 5773 (2021).

Poster session : C. Cornet, G. Bell, A. Trampert and F. Leroy
Authors : M. Kirti 1, M. Sütő 2, E. Tóvári 2, P. Makk 2, T. Prok 2, S. Csonka 2, P. Banerjee 1 , P. Rajak 1, R. Ciancio 1 , J. R. Plaisier 3 and G. Biasiol 1
Affiliations : 1: IOM CNR, Laboratorio TASC, Area Science Park Basovizza, 34149Trieste, Italy; 2: Department of Physics, Budapest University of Technology and Economics and Nanoelectronics “Momentum” Research Group of the Hungarian Academy of Sciences, 1111 Budapest, Hungary; 3: Elettra-Sincrotrone Trieste S.C.p.A., Area Science Park Basovizza, Trieste, 34149, Italy

Resume : The path to the implementation of quantum computers relies on the availability of suitable material platforms. Semiconductor-superconductor hybrid systems resulting in Andreev quantum bits (qubits) are among the promising candidates, as high-quality superconducting thin films with transparent interfaces to a low-D semiconductor will make it possible to improve the coherence time and strong qubit-qubit coupling [1]. In this work we have demonstrated that in-situ growth of Al films on near-surface InAs 2D electron gases (2DEGs) can be grown by Molecular Beam Epitaxy on GaAs substrates with quality comparable to state-of-the art growth on InP [2]. Adaptation of the metamorphic growth protocol previously adopted by us for In0.75Ga0.25As on GaAs (001) [3] allowed us to reach low-T electron mobilities up to 8X10^5cm^2/Vs in undoped deep InAs/In0.81Ga0.19As 2DEGs, while preserving values around 3.6X10^4cm^2/Vs for 2DEGs at 10nm from the surface, with a charge around 3.5X10^11/cm^2. Si doping allows tuning the charge density up to 1X10^12/cm^2, with mobilities up to 5.7 and 8.6X10^4cm2/Vs on VdP and Hall bar structures, respectively. Shubnikov-de Haas oscillations on Hall bar structures show well-developed quantum Hall plateaus with a single occupied subband, including Zeeman split-features at ν=3 and 5. In-situ growth of Al films was done at about -60C with a growth rate of about 0.5A/sec. AFM and X-ray reflectivity showed that Al deposition is conformal to the underlying semiconductors, preserving the cross-hatched pattern typical for metamorphic growth and a RMS roughness of about 1nm. Synchrotron radiation XRD rocking curves showed the existence of (111) Bragg peaks, though with intensity much weaker than Al grown on GaAs (001). XRD results will be complemented by cross-sectional TEM data to better assess the Al film crystalline properties. Resistivity measurements as a function of temperature on 10nm-thick films gave values of a few X10^-9Ωm at 4K and 2.5X10^-8Ωm at RT, comparable to the best Al layers on GaAs [4]. Superconducting proximity effect was observed in a Josephson junction. The observed phenomenology opens the way to the exploitation of Andreev physics on GaAs-based technology. 1. Lee, J. S. et al. Transport Studies of Epi-Al/InAs Two-Dimensional Electron Gas Systems for Required Building-Blocks in Topological Superconductor Networks. Nano Lett. 19, 3083–3090 (2019). 2. Wickramasinghe, K. S. et al. Transport properties of near surface InAs two-dimensional heterostructures. Appl. Phys. Lett. 113, 262104 (2018). 3. Capotondi, F. et al. Strain induced effects on the transport properties of metamorphic InAlAs/InGaAs quantum wells. Thin Solid Films 484, (2005). 4. Fan, Y.-T. et al. Atomic-scale epitaxial aluminum film on GaAs substrate. AIP Advances 7, 075213 (2017).

Authors : T. Steinhartova 1, N. Benali 1, R.H. Menk 2,3,4, A. Pilotto 5, F. Driussi 5, P. Palestri 5, L. Selmi 6, F. Arfelli 3,7, M. Cautero 2, M. Colja 2, G. Cautero 2,3, G. Biasiol 1
Affiliations : 1 IOM CNR, Laboratorio TASC, Area Science Park Basovizza, Trieste, 34149, Italy; 2 Elettra-Sincrotrone Trieste S.C.p.A, Area Science Park Basovizza, Trieste, 34149, Italy; 3 Istituto Nazionale di Fisica Nucleare, INFN, Sezione di Trieste, Trieste, 34100, Italy; 4 Department of Medical Imaging, University of Saskatchewan, Saskatoon, S7N 5A2, SK, Canada; 5 DPIA, University of Udine, Via delle Scienze 206, Udine, 33100, Italy; 6 DIEF, University of Modena and Reggio Emilia, Via Vivarelli 2, Modena, 44100, Italy; 7 Department of Physics , University of Trieste, Trieste, 34128, Italy

Resume : Avalanche photodiodes (APDs) detectors for synchrotron radiation have been traditionally based on silicon. GaAs-based APDs are however a promising alternative for particularly demanding applications for high energy, ultra-short pulsed light sources [1]. We developed GaAs/AlGaAs APDs with separated absorption and multiplication regions (SAM-APDs) [2]. The multiplication region is made of a staircase-like periodic bandgap modulation, which favors well defined multiplication of electrons and suppresses multiplication of holes (lower noise of device) [3]. The amplitude of this modulation, which determines multiplication efficiency and excess noise, is limited by the indirect AlxGa1-xAs bandgap at x>0.45. In previously fabricated devices, the staircase period consisted of GaAs and Al0.45Ga0.55As layers and a linearly graded AlxGa1-xAs region (0.45>x>0), grown by Molecular Beam Epitaxy (MBE). Numerical simulations showed that, for a given multiplication, a larger conduction band discontinuity in the first steps is beneficial to reduce excess noise [4]. In this work we have realized this concept by replacing GaAs with In0.2Ga0.8As in the first two steps. Due to the 1.5% lattice mismatch between GaAs and In0.2Ga0.8As, preliminary investigations were done to exclude lattice relaxation through dislocations. A set of samples was grown by MBE on GaAs (001) consisting of a 8.6nm InyGa1-yAs grading (0>y>0.2) followed by In0.2Ga0.8As of thicknesses ranging from 5 nm to 1 um. XRD, Raman spectroscopy and AFM experiments showed that the structures are strained and dislocation-free up to a critical In0.2Ga0.8As thickness of at least 60nm. Based on this, we fabricated a SAM-APD as in [3] where in the 2 initial steps the 35nm-thick GaAs layer was replaced by In0.2Ga0.8As and the graded region extended accordingly. We will show preliminary tests on multiplication efficiency and excess noise under illumination with a green laser. [1] G. Lioliou et al., Nucl. Instrum. Meth. A 813 (2016) 1. [2] F. Capasso et al., IEEE T Electron Dev. 30 (1983) 381. [3] T. Steinhartova et al., 2017 JINST 12 C11017. [4] A. Pilotto et al., IEEE T Electron Dev. 66 (2019) 1810.

Authors : A. Lysak, E. Przeździecka R. Jakiela, Z. Khosravizadeh, M. Szot, A. Adhikari, A. Kozanecki
Affiliations : Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, Warsaw, Poland

Resume : ZnCdO ternary alloys are being actively studied due to the possibility of energy band gap modification. The band gap shrinkage for Zn1–xCdxO from 3.1 eV to 1.8 eV is possible due to the presence of the CdO, in addition to the direct band gap (2.35 eV), two indirect band gaps 1.28 and 0.8 eV at room temperature. Also, doping with rare earth elements (Sm3 , Ce3 , Y3 , La3 , Nd3 and Eu3 ) allows manipulation of the optical characteristics of ZnO and CdO materials. Properties ZnCdO solid alloys doped with Eu are practically not studied. In this work we present the results of investigation of {ZnCdO/ZnO}30 multiple quantum wells (MQWs) doped with Eu deposited on quartz and on Si substrates. The {ZnCdO/ZnO}30 quantum structures were doped with Eu using the plasma-assisted molecular beam epitaxy (PA-MBE) method. The difference in the Eu concentrations in the samples was obtained by different temperatures of the europium effusion cell, as well as in the localization of Eu (in barriers or in the whole quantum structure). The obtained MQWs were annealing at various temperatures (700 and 900°C) in an O2 atmosphere for 5 minutes. Analysis of the depth composition and profile of elements (Cd, Eu, Zn and O) in MQWs was carried out by secondary ion mass spectrometry (SIMS) and the concentration of Eu before and after annealing was estimated. The distribution of Eu after annealing is uniform for all {ZnCdO/ZnO}30 MQWs, but its concentration is reduce. To study the effect of temperature on the band gap, the transmission spectra of as grown and annealed at 900 oC MQWs doped with Eu deposited on quartz substrates were measured in the range of 10-290 K. The post-annealing effect has a great influence on the MQWs transmission spectra was noted. For as grown MQW with a higher Eu concentration (9,38*1018 atoms/cm3), the band gap is 3.322 eV at low temperatures, while for as grown sample with a lower Eu concentration (3.59*1016 atoms/cm3), the band gap is about 3.268 eV. Due to a reduction in the Cd and Eu concentration in the annealed samples in both MQWs energy band gap shift (to 3.314 eV and 3.298 eV, respectively) were observed. For all structures, a blue shift of the band gap with increasing temperature was observed. The temperature dependence of the optical band gap of as grown and annealed {ZnCdO/ZnO}30 MQWs doped with Eu was investigated using the empirical Varshni and the Bose-Einstein (B-E) equations. The obtained fitting parameters from the two models are quite close to each other, however, it was noted that the B-E model is better represented the entire temperature range. This work was supported in part by the Polish National Science Center, Grants No. 2019/35/B/ST8/01937, and 2021/41/B/ST5/00216.

Authors : Laurent Pedesseau 1*, Lipin Chen 1, Ida Lucci 1, Divishth Gupta 1, Charles Cornet 1
Affiliations : 1 Univ Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082, F-35000 Rennes, France

Resume : The determination of absolute surface and interface energies of materials is one challenging issue in today’s epitaxial developments, as it fundamentally governs the nucleation and physical properties of heterogeneously integrated materials and devices for photonics, electronics or energy harvesting applications.[1] Especially, determining the hetero-interface absolute energies remain tricky, because of the difference of chemistry between the two materials considered. In this work, we use Density Functional Theory, with a fictitious hydrogen atoms charge compensation strategy, to determine the surface and interface absolute energies in the III-V/Si heterogeneous materials association case [1,2]. This method is expected to be applicable for all other heterogeneous materials association. We finally show how, in the specific case of III-V/Si heterogeneous epitaxy, it allows understanding structural properties of samples, and consider their use for applications in photonics, solar cells, or solar hydrogen production through water splitting [3,4]. This research was supported by the French National Research Agency PIANIST Project (Grant no. ANR-21-CE09-0020), and NUAGES Project (Grant no. ANR-21-CE24-0006). References: [1] I. Lucci et al., “Universal description of III-V/Si epitaxial growth processes” Physical Review Materials 2 (6), 060401, 2018 [2] I. Lucci et al., “A Stress-Free and Textured GaP Template on Silicon for Solar Water Splitting”, Advanced Functional Materials, 28(30):1801585, 2018. [3] M. Alqahtani et al., “Photoelectrochemical water oxidation of GaP1− xSbx with a direct band gap of 1.65 eV for full spectrum solar energy harvesting”, Sustainable Energy & Fuels 3, 2019. [4] L. Chen et al., Advanced Science 2022

Authors : Boris Croes, Fabien Cheynis, Yide Zhang, Cédric Voulot, Kokou Dodzi Dorkenoo, Salia Cherifi-Hertel, Cristian Mocuta, Michaël Texier, Thomas Cornelius, Olivier Thomas, Marie-Ingrid Richard, Pierre Müller, Stefano Curiotto, Frédéric Leroy
Affiliations : Aix Marseille Univ, CNRS, CINAM, AMUTECH, Marseille, France;Aix Marseille Univ, CNRS, CINAM, AMUTECH, Marseille, France;Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, Strasbourg, 67000, France;Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, Strasbourg, 67000, France;Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, Strasbourg, 67000, France;Synchrotron SOLEIL, L'Orme des Merisiers, St Aubin BP 48, F-91192 Gif Sur Yvette, France;Aix Marseille Univ, Univ Toulon, IM2NP, AMUTECH, CNRS, F-13397 Marseille 20, France;Aix Marseille Univ, Univ Toulon, IM2NP, AMUTECH, CNRS, F-13397 Marseille 20, France;Aix Marseille Univ, Univ Toulon, IM2NP, AMUTECH, CNRS, F-13397 Marseille 20, France;Univ Grenoble Alpes, CEA Grenoble, IRIG, MEM,NRS, 17 Rue Martyrs, F-38000 Grenoble;Aix Marseille Univ, CNRS, CINAM, AMUTECH, Marseille, France;Aix Marseille Univ, CNRS, CINAM, AMUTECH, Marseille, France;Aix Marseille Univ, CNRS, CINAM, AMUTECH, Marseille, France

Resume : Among ferroelectrics a new class of materials with high potentialities for spintronic applications has recently been introduced as ferroelectric Rashba semiconductors[1,2]. Main results, obtained on GeTe thin films, have demonstrated that the reversal of the ferroelectric polarization under an electric field leads to a consistent change of the spin chirality of the band structure[3,4]. An effective spin-to-charge conversion has also been demonstrated in a ferromagnetic-GeTe heterostructure[5-7] and a nonreciprocal charge transport up to room temperature has been detected[8]. However the influence of the domain structure on these phenomena still remains unclear. Given the rhombohedral structure of GeTe (R3m space group) and the existence of an electric dipole in the <111> direction, eight possible polar domain orientations are anticipated in this system. In spite of the growing interest in such ferroelectric Rashba semiconductors[9], the detailed polar domain structure and spatial organization has not been studied so far. These studies are a prerequisite for the controlled switching of ferroelectric domains and the understanding of aging properties. In this presentation we will address the ferroelectric nanodomains organization of GeTe thin films grown on Si(111)[10], the domain wall type, and the structure of the interface with the substrate. As reported by Wang et al.[11], quasi-single crystalline GeTe thin films can be grown on Si(111) by molecular beam epitaxy using a pre-deposition of 1 monolayer (ML) of Sb onto the substrate. It is an ideal platform to study and control ferroelectric domains as they are no more limited by grain boundaries. We have determined by X-ray diffraction (3D reciprocal space maps) in combination with low energy electron microscopy (LEEM) the volume fraction of the ferroelectric domains and the domains size in a large range of film thickness (10-1800nm). Second harmonic generation (SHG) microscopy combined to polarimetry analysis reveal the local symmetry of these domains. Using high resolution transmission electron microscopy (HR-TEM) we show that domain walls are only of 71° and that the GeTe/Si interface is stabilized by misfit dislocations that relax the large lattice parameter mismatch between both lattices. The reversible decay/growth of the ferroelectric nanodomains under annealing/cooling, as demonstrated by in situ LEEM, is attributed to the thermal stress induced by the large difference of linear thermal expansion coefficients of both materials. [1] D. Di Sante et al., Adv. Mater. 2013, 25, 509. [2] M. Liebmann et al., Adv. Mater., 2016, 28, 560. [3] C. Rinaldi et al., Nano Lett., 2018, 18, 2751. [4] J. Krempasky et al., Phys. Rev. X, 2018 8, 021067. [5] C. Rinaldi et al., APL Mater., 2016, 4, 032501. [6] J. Slawinska et al., Phys. Rev. B., 2019, 99, 075306. [7] S. Varotto et al., Nature Electron. 2021, 4, 740 [8] Y. Li et al., Nat. Commun., 2021, 12, 540 [9] S. Picozzi, Frontiers in Physics, 2014, 2, 10. [10] B. Croes et al., Phys. Rev. Mater., 2021, 5, 124415. [11] R. Wang et al., J. Phys. Chem. C, 2014 118, 29724. Acknowledgments: The authors thank funding from Excellence Initiative of Aix-Marseille University A*MIDEX, a french "Investissements d'Avenir" program through the AMUtech institute. This work has also been supported by the ANR grants HOLOLEEM (ANR-15-CE09-0012) and TOPELEC (ANR-18-CE92-0052)

Authors : A. Adhikari, A. Lysak, A. Wierzbicka, J. M. Sajkowski, R. Jakiela, K. Zeinab, E. Przeździecka
Affiliations : Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, Warsaw, Poland

Resume : Oxide semiconductors are promising candidates for optoelectronic applications because of advantages like large bandgap energy, high mechanical and chemical stability. Among the oxide semiconductors, group-II oxides have been increasing interest as they share similar features with group-III nitrides. CdO is one of the oldest known semiconductor oxides that have been studied widely because of its high electron concentration, high transparency, high electron mobility, low resistivity, and high exciton binding energy. However, a relatively low bandgap of CdO, which is 2.3 eV (at the ambient condition), along with two indirect band gaps of 1.2 eV (Σ3 and Γ1) and 0.8 eV (L3 and Γ1), restricts its use only in the visible wavelength range of applications. Development of advanced growth techniques and in situ characterization methods allowed not only to grow high quality CdO layers but also related ternary alloys (such as ZnCdO and CdMgO) which in turns can be used in many wide spectral range applications. Among many growth techniques used to grow CdO layers, plasma-assisted molecular beam epitaxy (PA-MBE) allows most precise control of growth parameters, such as growth rate, flux of Cd, which could be monitored by a variety of in situ characterization techniques such as flux monitor, laser reflectometry, and desorption mass spectroscopy. In this work we have investigated a series of CdO layers grown on m-plane sapphire substrate using PA-MBE technique. CdO layer on m-plane substrate have a strong preferential <110> orientation. During the growth process, the oxygen flow and power of oxygen plasma was fixed and Cd flux was changes and controlled by varying the temperature of Cd effusion cell. The growth rate was estimated in situ using laser reflectometry. The relation between Cd and O2 parameters during growth influences on the stoichiometry of the CdO layers. As a results we have a chance to analyze samples grown in O-rich and in Cd-rich condition as the Cd effusion cell temperature increases from 370ºC to 430ºC. The change in stoichiometry of CdO layers from O-rich to Cd-rich condition affects morphological, optical and electrical properties which is manifested in roughness parameter, optical bandgap and electrical conductivity of corresponding layers. Surface morphology of CdO layers were studied using scanning electron microscope (SEM) and atomic force microscope (AFM) techniques. The optical transmittance and bandgap of CdO layers were investigated using UV-Vis spectroscopy at room temperature. These results will provide importance of growth parameters of CdO layers during the growth process, which subsequently leads to more accurate control of quantum structures and CdMgO and ZnCdO ternary alloys towards new optoelectronic devices. The work was supported by the Polish NCN project DEC-2021/41/N/ST5/00812, and DEC-2021/41/B/ST5/00216.

Authors : Tadeá? Hanu?, Bouraoui Ilahi, Javier Arias?Zapata, Alexandre Chapotot, Abderraouf Boucherif
Affiliations : Tadeá? Hanu? 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada ;Bouraoui Ilahi 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada ;Javier Arias?Zapata 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada ;Alexandre Chapotot 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada ;Abderraouf Boucherif 1: Institut Interdisciplinaire d?Innovation Technologique (3IT) Université de Sherbrooke, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada 2: Laboratoire Nanotechnologies Nanosystèmes (LN2) - CNRS IRL-3463, 3000 Boulevard de l?Université, Sherbrooke, J1K 0A5, QC, Canada

Resume : High-quality crystalline semiconductor free-standing membranes (SFSM) of functional materials are of paramount importance for fundamental research and device applications. Compared to classical substrate-bound structures, SFSM form offers extra degrees of freedom for implementations that cannot be provided by traditional hetero-integration techniques. Furthermore, SFSM of various materials can be stacked, enabling easy coupling of physical properties between dissimilar materials. Additionally, the freestanding form makes these structures lightweight and flexible. Using SFSM for the device production instead of bulky wafers provides significant cost saving through multiple reuses of the same substrate, especially for non-silicon-based materials with orders of magnitude higher prices. Accordingly, new emerging techniques such as Van der Waals epitaxy [1] and remote epitaxy [2], using 2D materials (graphene, hexagonal boron nitride, etc.) as weak bonding interface, show huge potential for the fabrication of various SFSM. Nevertheless, those methods are still in the early stages of development, especially those targeting large-scale production, compared to other techniques such as nanostructured substrates [3,4] or epitaxial lift-off [5]. In this work, we demonstrate the formation of homogenous edge-to-edge porous Ge (PGe) layers on industry-standard 100 mm wafer-scale by bipolar electrochemical etching with the ability to modulate the corresponding thickness and porosity. These PGe nanostructures maintain high material purity and substrate crystal orientation with excellent surface conditions suitable for epitaxial growth. Moreover, we study the initial stages of epitaxial growth on porous substrate. Morphological evolution shows the transition from 3D nucleation on nanostructured substrate towards the coalescence of the layer and continuous 2D growth. The growth of ultra-thin Ge layers on top of PGe substrate is demonstrated. This Ge epilayer is easily detachable due to the nanostructured PGe interface. Our findings lay the groundwork for the wafer scale production of free-standing monocrystalline Ge membranes for applications in light and flexible optoelectronics. [1] Y. Kobayashi et al., Nature 484, 223?227 (2012) [2] Kim, Y., et al., Nature 544, 340?343 (2017) [3] Park et al., Joule, vol. 3, p. 1782?1793 (2019) [4] A. Boucherif et al., Appl. Phys. Lett., vol. 102, p. 011915, no. 1 (2013) [5] A. van Geelen et al., Mater. Sci. Eng. B, vol. 45, (1997)

Authors : Stetsyuk T.1, Malyshev V.2, Gab A.2, Shakhnin D.2, Yovenko A.2
Affiliations : 1 Frantsevich Institute for Problems of Materials Science of NAS of Ukraine, 2 Open International University of Human Development “Ukraine”

Resume : To deposit Mo2C and W2C coatings onto different non-oriented metal substrates, electrolysis of Na2WO4-based oxide melts was applied. In such a case, it is necessary to obtain continuous cathode deposits with preset properties (structure, orientation, and crystallite size). During electrolysis, an important role is played by the initial stages of crystal nucleation. The initial stages of crystal nucleation were studied by the electrochemical methods used in the study of phase formation with simultaneous investigation of the microstructure of the substrate surface and electrolysis products. The initial stages of the nucleation of Mo2C and W2C crystals in tungstate-molybdate-carbonate melts of a certain composition on Ag, Au, Cu, Pt, and Ni substrates were studied by electrodeposition method depending on the electro-crystallization conditions: temperature, deposition duration, initial current pulse, and current density. It was found that the first crystals start growing immediately after the appearance of the peak on the switching curves. The repeated switching-on the current within a short period of time (5–10 s) does not give rise to peaks formation. These facts indicate that the crystallization overvoltage is associated with three-dimensional nucleation. From the experimental results, the crystallization overvoltage values were evaluated appearing due to a considerable energy loss for synthesis components nucleation at the first moments of synthesis. These values at the Ag electrodes within the temperature range 973–1023 K are 8–40 mV. During the metal carbides deposition onto the same metals substrates was not accompanied by crystallization overvoltage. This overvoltage took place only at low values for metals with high exchange current. Under these conditions, the surface diffusion stage does indeed limit the electrode process rate. With an increase of the carbide deposition rate, the number of crystallization centers increases, reducing decelerations caused by surface diffusion. As a result, with higher overvoltages, the limiting stage is seemingly changed so that the process rate is determined either by the electron transfer rate or by the rate of diffusion from the melt volume. It is characteristic that the height of the overvoltage maximum peaks for the abovementioned metals is proportional to the reciprocal time of their formation. This seems to be associated with the penetration of the part of the deposited components into the substrate bulk due to solid-phase diffusion and allows to qualitatively characterize the degree of inertness of the substrate material. The experimental study of the initial stages of Mo2C electrocrystallization from the tungstate–molybdate–carbonate melts with the electrodes made from various materials over a wide temperature range allows to put forward the following concepts of nucleation. Thus, for example, with the inert substrates at T < 1073–1173 K, considerable crystallization hindrances were observed associated with the formation of three-dimensional nuclei. An increase in the electrolysis temperature facilitates diffusion of the components atoms into the substrate resulting in a decrease of the crystallization overvoltage. Simultaneously, a transition from the three- to two-dimensional nucleation is observed and, in some cases, to depolarization phenomena due to solid-phase saturation of the electrode boundary layers with the synthesis components (molybdenum and carbon) and to the formation of an alloy with the electrode material.

Authors : Iwona Pasternak, Walery Kołkowski, Włodek Strupiński
Affiliations : Vigo Photonics, Poland, 05-850 Ożarów Mazowiecki, ul.Poznańska 129/133

Resume : QCLs (quantum cascade lasers), InGaAs 1.7 and ext-PDs (extended InGaAs photodetectors) are very attractive materials for use in sophisticated photonics and microelectronics such as optical recording, scanners, laser spectroscopy, thermal or gas sensing. Once a novel laboratory curiosity, QCLs and ex-PDs are now becoming commercially available products, shaping new and exciting applications. Optical wireless power transmission (OWPT) is another exciting field. Photovoltaic devices able to convert not only sunlight but also laser power offer new promising technological capabilities. These Optical Power Converters (OPCs), also called Laser Power Converters (LPCs), have been used for power links and radio-over-fiber, long-distance and safe laser power beaming, power electronics, and other applications. In this work we present the intricacies and challenges of the development and industrial production of MOCVD-grown QCLs, VCSELs, LW-VCSELs, PVCs (solar cells and lasers) EELs (edge emitting lasers for use in telecommunication) and ext-PD structures, fabricated in Vigo Photonics. Different types of epitaxial structures were grown using AIX 2800 G4 production system, in 12 x 3” or 4” wafer configuration per growth run. Structural and electrical properties of epitaxial layers were examined using X-ray diffraction (XRD), high resolution secondary ion mass spectroscopy (HRSIMS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), electrochemical capacitance-voltage technique (ECV), mapping of photoluminescence (PL) and others. AIX 2800 G4 production reactor, whose processes are characterized by highly complicated chemical reactions, enables development of sophisticated epitaxial structures. In multi-wafer reactor chambers, gas residence is much longer when compared with small R&D systems and the growth zone is much larger. As a consequence, in case of QCLs, the hetero-interfaces of InGaAs/InAlAs are inevitably graded, which negatively impacts optical and electrical parameters of QCL devices. In addition, QCL structure requires the exact layer thickness as well as absolute precision and repeatability in the development of strained InAlAs and InGaAs epi-layers. In case of ext-PDs fabrication, the crucial thing is to develop a specially designed and graded buffer layer and try to avoid numerous misfit defects and anomalies in dark current. The challenge in OWPTs epitaxial layers development is to achieve not only higher conversion efficiency, but also higher output powers. We consistently improve MOCVD technology by enhancing capability and flexibility in terms of alloy composition, dopant, and thickness control, within-wafer uniformities and reproducibility, and by optimising thermal budget, which results in higher interface quality. We succeeded in obtaining high crystallographic quality and repeatability of the epi-layers, leading to QCL high optical power (>2W), ext-PDs high-performance operation with low dark current density (less than 1E-4 A/cm2 at -100mV/RT) and high quantum efficiency. VCSEL, LW-VCSEL and EEL lasers displayed high optical parameters due to nanometer-scale thickness control and optimization of strain and efficiency of quantum wells. Acknowledgements This research was supported by The Polish National Centre for Research and Development grant MAZOWSZE/0032/19-00.

Authors : Anna Capitaine, Muhammad Luthfi Fajri, Peeranuch Poungsripong, Olivier Margeat, Beniamino Sciacca
Affiliations : Aix-Marseille Univ, CINaM; Aix-Marseille Univ, CINaM; Aix-Marseille Univ, CINaM; CNRS, CINaM; CNRS, CINaM

Resume : High-quality monocrystalline materials and nanostructures are key to high-efficiency optoelectronic devices (Polman et al., Science, 2016), plasmonic materials (Wu et al., Adv Mater, 2014) and metasurfaces (Koenderink et al., Science 2015). A large variety of materials can be synthesized at low temperature in solution as colloidal single crystals, combining the advantages of high-quality material, low-cost fabrication, and potential for large area integration into nanophotonic and plasmonic devices, but are typically limited to Platonic solid shapes. We recently demonstrated that colloidal single-crystal gold nanocubes, could be used as building blocks for the fabrication of continuous monocrystalline nanostructures via liquid-phase epitaxy of adjacent nanocubes at near ambient temperature (Capitaine et al, Adv Mater., 2022). This consitutes a remarkable example that bridges the gap between bottom-up and top-down approaches. We demonstrate here that the strategy developed for gold nanocube epitaxy, can serve as a model for other noble metals, such as silver. We investigate similarities and differences in the epitaxy mechanism of single-crystal silver nanocubes by performing a set of ex-situ and operando optical experiments on a nanocube dimer model system and comparing the results to FDTD simulations. Monodisperse 40 and 50-nm Ag single-crystal nanocubes are first synthesized in solution by polyol synthesis. Next, using capillary forces they are self-assembled in a polydimethylsiloxane (PDMS) mould containing pre-defined traps, with individual nanocube subunits lying face-to-face in a dimer configuration. Then nanocubes are epitaxially connected and transformed into continuous monocrystalline at low temperature by inducing an equilibrium between nanocube etching and growth in an aqueous acidic medium in the presence of a silver salt. The insights gained via this model system about the chemical framework for nanocube epitaxy is then exploited to control the epitaxial welding of larger complex structures such as curved lines assembled by capillary forces and closely-packed Langmuir-Blodgett films on PDMS for the first time, showing that this unique approach is highly versatile for the fabrication of monocrystalline silver nanostructures. We use high-resolution transmission electron microscopy and electron backscatter diffraction to provide evidence for epitaxy and study the impact of nanocube misalignment. Finally, we show that such nanostructures and thin films can be transferred from PDMS to various substrate by contact printing. This paves the way for swift integration into optoelectronic devices of high-quality monocrystalline silver mirrors, contacts and/or large-scale nanophotonic surfaces. This is particularly relevant for devices that are incompatible with classic nanopatterning strategies such as perovskite layers.

Authors : L. D. Filip, A.G. Boni, C. Chirila, C. Radu, I. Pasuk, I. Pintilie, l. Pintilie
Affiliations : National Institute for Materials Physics, Atomistilor Str., no. 405A, Magurele, Romania

Resume : Ferroelectric materials can be used as a negative capacitance element at the gate of a field effect transistor with the purpose of decreasing the fundamental limit of subthreshold swing of 60mV/decade. Many investigations have been performed in the last years for understanding both NC dynamic regime during polarization switching but also the possibility of stabilization of a steady-state NC in FE multilayers and superlattices. The present study evaluates switching characteristics of the FE/isolator/FE multilayered thin films structures exhibiting multiple polarization states. Ferroelectric PZT thin films are used intercalated by SrTiO3 or BaTiO3 isolator layers. All structures are epitaxial grown by pulsed laser deposition and the structural quality is investigated by X-ray diffraction and TEM microscopy. The negative capacitance dynamic regime is investigated during atypical step-like switching and we also evaluate the possibility to stabilize a negative capacitance steady state in the intermediate polarization states. The experimental investigations were doubled by numerical calculations using density functional theory (DFT). In order to simplify the problem, the PbTiO3 ferroelectric material was chosen and the PTO/STO/PTO multilayer structure was constructed. In this configuration the individual polarization of each layer was prepared in several arrangements: both polarizations having the same direction (representing the polarization saturation case) or both polarizations pointing towards each other or away from each other (representing the intermediate polarization state). The structures were structurally relaxed and it was evidenced that for the intermediate state one of the layers evolved towards an almost centrosymmetric state with a near zero polarization. This is a finger print of a steady-state negative capacitance state.

Authors : Philip J. Mousley, Christopher W. Burrows, Chris Nicklin, Gavin R. Bell
Affiliations : Diamond Light Source, UK; University of Warwick, UK

Resume : Surface X-ray diffraction (SXRD) is a powerful structural probe for epitaxial thin films. Sb(0001) ultrathin films in tensile strain have been grown by molecular beam epitaxy on InAs(111)B substrates and their detailed atomic structures derived using SXRD. Features considered in the structural modelling include interfacial intermixing, surface roughness, individual layer relaxations, and rotational twin domains. A four-bilayer film showed significant structural relaxation in every layer, while a 19-bilayer films showed consistent "bulk" relaxation with strongly modified relaxations in layers near both the surface and interface. Both films included rotational twin domains and interfacial mixing over <3 atomic layers depended on the growth history.

Authors : Gavin R. Bell, Ibrahim Elhoussieny, Christopher Benjamin, Thomas Rehaag
Affiliations : University of Warwick, UK

Resume : Molecular beam epitaxy (MBE) has been used to grow several topologically nontrivial materials involving In, Bi, Sb, Sr and Mn. Analysis of the films using X-ray photoelectron spectroscopy (XPS) provides valuable information towards growth optimisation. The results of in situ XPS (in a chamber connected to the MBE system), XPS via vacuum suitcase transfer, and XPS via air transfer will be discussed. For Mn- and Sr-containing materials, their very high sensitivity to surface contamination strongly favours in situ or vacuum suitcase transfer.

Authors : Yu Liu, Sivert Dagenborg, Damian Braozowski, Magnus Nord, Ingrid Hallsteinsen
Affiliations : Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim, Norway; Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway

Resume : The geometrical strain engineering of magnetic perovskite thin films enables rich magnetic properties that are yet to be fully explored. One route to obtain these complex magnetic thin films is to use substrates with different surface geometries and anisotropic strain states. (111)-orientated SrTiO3 used in this work has hexagonal surface geometry that provides magnetic thin films with unique anisotropic strain and high oxygen octahedral connectivity compared to STO (001), in which the magnetic states are highly tuneable by external influences such as temperature and magnetic fields. The magnetic domain configurations in addition to structural information can be imaged by Scanning transmission electron microscopy-differential phase contrast (STEM-DPC) technique directly and can be coupled with in-situ temperature and field control. A prerequisite for this technique is the need for high quality plan-view magnetic samples over a large area. La0.7Sr0.3MnO3 (LSMO) is a widely reported room temperature ferromagnet, making the material ideal for in-situ STEM-DPC study. In this work we use LSMO epitaxial grown by pulsed laser deposition on STO (111) substrate as a model system for in-situ STEM-DPC study. Thin film characterisation reveals by layer growth by RHEED, and fully single crystalline epitaxy confirm with XRD. The sample was also characterised by vibrating sample magnetometer confirming the presence of room-temperature ferromagnetism. The TEM plan-view sample was prepared by both conventional tripod polish in combination with focused ion beam (FIB) and solely FIB. A comparison is made on different methods in term of preparation difficulties and sample quality. The conventional tripod polish utilises a wedge polish method with final thinning in FIB. Meanwhile, for solely FIB preparation the bulk sample uses a conventional lift-out method, but optimised for a larger surface area. The bulk is then mounted to a TEM grid holder on pin, where the lift-out grid is lying flat instead of upright on the holder and thinned down to electron transparent. The use of alignment marks enables one to perform precision mounting to the holder and corrections in the tilt during thinning. Using STEM-DPC we correlate structure and magnetic properties, and the effect of the different sample preparation routines.

Authors : Evelina Dudutienė, Algirdas Jasinskas, Monika Jokubauskaitė, Sandra Stanionytė, Martynas Skapas, Arnas Naujokaitis, Bronislovas Čechavičius, Renata Butkutė
Affiliations : State Research Institute Center for Physical Sciences and Technology

Resume : GaAsBi/GaAs multiple quantum wells (MQW) are promising candidate to be used as an active area in near infrared GaAs-based lasers or LEDs due to unique properties, such as, fast bismuth incorporation induced band gap reduction, increase in spin-orbit splitting and less temperature sensitive band gap. However, the growth of high optical quality GaAsBi quantum well (QW) layers is still a challenge. One of the methods to grow high quality GaAsBi MQWs is two-substrate-temperature molecular beam epitaxy (MBE) technique. In this work five periods of GaAsBi/GaAs MQW grown by molecular beam epitaxy using conventional single-substrate temperature (SST) and two-substrate-temperatures (TST) techniques are compared. In the SST mode, the substrate temperature was set to 370 °C for growth of both GaAsBi QW and GaAs barrier layers. In the TST growth mode, the substrate temperature was set to 370 °C for GaAsBi layers and higher temperature of about 450 °C - for the growth of GaAs layers. The structural and optical characterisation of GaAsBi/GaAs MQW was carried out. X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) indicated higher structural quality of GaAsBi/GaAs MQW structures grown using SST technique. The intensities of photoluminescence (PL) at room temperature were comparable for both MQW structures. However, the temperature-dependent PL measurements revealed that optical quality of MQW structures grown using TST technique is higher than MQW structures grown using conventional one-temperature MBE growth. PL peak position and full-width-at-half-maximum (FWHM) variation with temperature showed high carrier localisation of GaAsBi/GaAs MQW structure grown using SST technique. Moreover, the much faster PL intensity quenching, especially at low temperatures, of MQW grown using SST mode in comparison to TST-grown MQW was observed. High room temperature PL intensity of SST-grown GaAsBi/GaAs MQW was explained by decreased photoexcited carrier mobility due to localisation effect. The estimated scale of randomly distributed field fluctuations for SST grown MQWs was around 25 meV, comparable with thermal energy of carriers at room temperature.

Authors : R. KALVIG (1), E. JĘDRYKA (1), M. WÓJCIK (1), M. PETIT (2), L. A. MICHEZ (2)
Affiliations : (1) Institute of Physics PAN, Al. Lotników 32/46, 02-668 Warsaw, Poland (2) Aix Marseille Univ, CNRS, CINAM, Marseille, France

Resume : Mn5Ge3(001)/Ge(111) epitaxial films (hexagonal D88 structure, space group P63/mcm) attracted a lot of interest as a potential source of polarized carriers into Ge, making them directly compatible with the mainstream silicon technology. This material reveals also a strong uniaxial magnetocrystalline anisotropy creating the opportunity to combine spintronics with the data storage. For practical applications it is interesting to add some carbon admixture, which boosts the Curie temperature of the Mn5Ge3Cx films from 296 K for x=0 up to 445 K for x=0.5. Unfortunately, doping with carbon leads to a significant drop of magnetocrystalline anisotropy constant Ku. The ferromagnetic resonance study performed at 15 K reveals the change of Ku from 5,97 ∙ 10^5 J/m3 in Mn5Ge3 down to 8,06 ∙ 10^4 J/m3 in the Mn5Ge3C0.5 film. To investigate the microscopic origin of this spectacular drop of magnetocrystalline anisotropy we performed the 55Mn NMR study in the entire carbon concentration range. Our previous NMR study performed on the 300 nm film with x=0.2 [1] has shown that carbon enters interstitially in the vicinity of the (6g) crystallographic positions, occupying the (2b) octahedral voids and reducing the magnetic moment of Mn atoms in the corners of a host octahedron by 0.7μB. The orbital moment anisotropy of (6g) Mn - measured as a difference between its value along the hexagonal c-direction and in the c-plane - dropped from 0.151μB for x=0 down to 0.058μB for x= 0.2. This change was postulated to be at the origin of the reduced magnetocrystalline anisotropy of the Mn5Ge3C0.2 film [1]. In this study we extend the 55Mn NMR study to a full carbon concentration range. We find that the hyperfine field anisotropy in the (6g) Mn sites continues to drop as a linear function of the carbon content. These results show that the main mechanism responsible for the observed drop of the uniaxial magnetocrystalline anisotropy upon carbon doping consists in a rapid increase of the carbon-affected Mn sites, prompted by the highly ordered carbon incorporation into the Mn5Ge3 crystal lattice [2]. They also confirm the scenario of a single ion origin of magnetocrystalline anisotropy in these compounds. References: [1] R. Kalvig, E. Jędryka, M. Wójcik, G. Allodi, R. De Renzi, M. Petit and L. Michez, Phys. Rev. B 97, 174428 (2018) [2] R.Kalvig, E. Jędryka, M. Wójcik, M. Petit and L. Michez, Phys. Rev. B 105, 094405 (2022)

Authors : G. Benvenuti, E. Wagner, W. Maudez
Affiliations : 3D-Oxides, 41 rue Henri Fabre, 01630 St Genis Pouilly

Resume : Sybilla equipment is addressing many of the challenges faced by the very promising and expanding field of oxide thin film deposition. Chemical Beam Epitaxy (CBE) enables deposition of multi-element oxides (up to 5 possible), either homogenously or in combinatorial mode (i.e with controlled precursor flow gradient emitted onto the substrate, in good agreement with theoretical model predictions). High homogeneity films +/-1% can be achieved, even on large substrates (450 mm wafer will be shown). Precursor decomposition can be initiated either thermally (substrate heating) or by irradiating with energetic beams (laser and electron activations were studied). Additive growth can be obtained by such localized irradiation, or alternatively depositing through shadow masks and benefiting from the line-of-sight nature of the technique (and exploiting the precursor decomposition kinetics not to damage masks). The multi-parameter nature of the deposition technology (precursor nature, different flows, temperature) allows to tune growth rate (from few nm/h to several um/h) as well as thin film physico-chemical properties (chemical composition, film morphology, crystallinity, etc.) and functional properties. Combinatorial growth reveals a very efficient facility to optimize processes (in one shot, saving time and resources) and address new thin film architectures. Some epitaxially grown materials such as TiO2 and LiNbO3 will be presented.

Authors : A. Ozcan-Atar (1), A. Gocalinska (1), P.P. Michalowski (2), D.D. Vvedensky (3), E. Pelucchi (1)
Affiliations : (1) Tyndall National Institute, University College Cork, Cork,Ireland ; (2) ?ukasiewicz Research Network, Institute of Microelectronics and Photonics, Warsaw, Poland ; (3) The Blackett Laboratory, Imperial College London, London, United Kingdom

Resume : Metal Organic Vapor Phase Epitaxy (MOVPE) is a well-established tool for producing high quality epitaxial films for many optoelectronic device components. Despite the extensive technological use of MOVPE, there are still a large number of unresolved issues. One of the major outstanding technological issues, linked to fundamental aspects of epitaxial growth processes, is the ?leakage? of p-type dopant Zn into surrounding III-V regions during the growth process. The lack of controllability of Zn incorporation and diffusion processes in III-V layers hinders the possibility of developing all III-V integration platforms, with multi-device stacking, or just even reliable simple inverted lasers with a p-i-n structure instead of the usual n-i-p design. Here, we report a finding on Zn diffusion, which remained hidden despite around 40 years of research on the topic. Zn is reported to have a relatively high diffusivity in InP at temperatures greater than 500°C, i.e. typical process temperatures of MOVPE. The diffusion of Zn has been heavily studied, especially looking at back-diffusion (opposite to growth direction), but remarkably studies in the growth direction are either lacking/few or the issue is addressed as part of more complex interplayed structures. To examine the Zn dopant behaviour in the growth direction, we grew a very simple structure: 200 nm Zn doped InP layer sandwiched between two undoped layers. Secondary Ion Mass Spectroscopy (SIMS) results show that Zn exhibits an asymmetric dopant concentration profile and appears for an unexpected ~1500 nm into the undoped layer in the growth direction. The diffusion in the opposite of the growth direction is more modest and can be accurately explained by well-known diffusion laws. However, in the growth direction the concentration profile is significantly different from what would be expected from diffusion processes alone. A comparative experiment with GaAs-based materials shows similar, but less extensive post growth tail, demonstrating also that the carry-over of Zn in InP is not a reactor memory effect, but is a material specific phenomenon. We have developed a model combining Fick?s second law of diffusion and material incorporation mechanisms together to understand Zn concentration profiles in InP layers. The tailing in the growth direction is modelled based on the assumption that either Zn (or the precursor DEZn) acts as a surfactant accumulating on the surface layer and gradually continues to incorporate into InP after the Zn source has been shut off. We used the Crank-Nicholson algorithm to numerically calculate this behavior with a finite difference approach which requires a set of boundary conditions which dynamically evolve to mimic the accumulation of the materials on the sample surface. The dopant concentration depth profiles that we have simulated with this method agree very well with the SIMS results. We will discuss in detail our experimental results and simulations, and our unique solution to the Zn diffusion problem. This will include Zn diffusion and accumulation behavior in a variety of other III-V materials, and a discussion of major consequences for III-V device design. The results of this work can enable growth designs for novel inverted laser structures and multicomponent devices, and broadly eliminate existing constraints while opening for new technological solutions.

Authors : Cristina Florentina Chirila, Georgia Andra Boni, Viorica Stancu, Iuliana Pasuk, Lucian Trupina, Lucian Dragos Filip, Cristian Radu, Ioana Pintilie, Lucian Pintilie
Affiliations : National Institute of Materials Physics, Atomistilor 405A, Magurele, Romania

Resume : Ferroelectric materials with perovskite structure, with ABO3 formula, are used in a wide variety of applications due to their multiple functional properties including the spontaneous polarization that can be manipulated by various stimuli: electric fields, temperature, mechanical stress and light. Ferroelectric layers are used in many electronic and sensing applications, such as ferroelectric field effect transistors, negative capacitance field effect transistors or pyroelectric infrared detectors. Here we present effects induced by doping on A or B positions of epitaxial Pb(Zr,Ti)O3 (PZT) thin films with Zr/Ti ratio of 20/80. This material is widely used due to the large value of polarization, reaching about 1C/m2, and to the fact that high quality epitaxial films can be obtained on single crystal SrTiO3 substrates by using the pulsed laser deposition (PLD) method.Th e PZT films were deposited by PLD from in-house produced targets using precursor metal oxides of at least 99.99 % purity. In order to obtain n doping, the target was doped with about 1 % Nb, Bi or La and for p doping 1 % Fe or K was introduced. The choice of doping species was not random but was guided by DFT calculations. We studied the effect of doping on the PbTiO3 structure (we chose PTO in order to simplify the numerical problem) using a large super cell obtained from 3x3x3 PTO unit-cells. A single Ti or Pb atom was replaced by either Nb, Bi, La, Fe or K, to obtain approximately 3.7% doping concentration. First we deposit thin films from doped targets to compare to that obtained from un-doped target. Then to produce bi-layer structures by successive deposition of one n-type PZT layer and one p-type PZT layer, with the aim to obtain a p-n ferroelectric homojunction. It was found that these p-n structures present polarization hysteresis and butterfly-shaped capacitance-voltage (C-V) characteristics, as for a ferroelectric capacitor, although the current-voltage (I-V) characteristics of the bi-layer structures are symmetric and linear as for a resistor. Moreover, it was found that the capacitance of the bi-layer structure is larger than that of the component layers. This is the signature of a stabilized negative capacitance effect. In summary, a relatively low doping concentrations can trigger significant differences in the macroscopic properties of epitaxial PZT films, although the structural properties are similar. The differences can be explained by different electronic properties induced by doping that acting as acceptor, and or doping that acting as donors. The p-type doping or n-type doping are evidenced by the special poling procedure used in PFM investigations. Results open new perspective in obtaining genuinely ferroelectric p-n homojunctions.

Authors : L. Ghimpu1, V. Suman1, D. Rusnac 2, D. Timpu3, T.Potlog2
Affiliations : 1Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, 1Physics Department and Engineering, Moldova State University, Chisinau, Moldova 3"Petru Poni" Institute of Macromolecular Chemistry, Iasi, Romania

Resume : A number of previous publications reveal that many composite semiconductor oxides have better gas sensitivity than a single semiconductor metal oxide. Both titanium oxide (TiO2) and zinc oxide (ZnO:Al) are wide band gap n-type semiconductors, their band gap energies are similar to each other (about 3.2-3.4 eV), and they both possess good gas sensing properties. In this paper, the TiO2:Nb thin films were reactively sputtered on glass and ZnO:Al/glass substrates, with the resistivity of 1.7 × 10− 4 Ω⋅cm, an transmittance of about 90%, mobility of 25 cm2/V∙s and a thickness of 400 nm. TiO2:Nb thin films were prepared at different temperature by RF magnetron sputtering at 100 W RF power. The distance from sample to the target was 6–7 cm. The working pressure was maintained at 4 × 103 Pa. The crystallographic structures of the TiO2:Nb thin films were studied via X-ray diffraction) method. Before annealing in vacuum the TiO2:Nb thin films show both polycrystalline and amorphous phases. Annealing in vacuum atmosphere showed substantial improvement of structural properties of TiO2:Nb thin films. The EDX spectra indicate the presence of Ti, Zn, and O elements. The Ti:Zn atomic contents in the thin film depends of the substrate temperature. The gas sensing properties are characterized in term of resistance and gas-sensing response. The gas sensing properties of ZnO/TiO2 RF composite thin films toward acetone and ethanol will be discussed in function of the substrate temperature.

Authors : Arkadiusz Ciesielski, Jakub Rogoża, Piotr Wróbel, Jan Pawłowski, Johannes Binder, Roman Stępniewski, Andrzej Wysmołek
Affiliations : University of Warsaw, Faculty of Physics, Pasteura 5, 02-093 Warsaw, Poland

Resume : Recent research regarding Boron Nitride (BN) layer growth focuses on the fabrication of the BN films with sp2 orbital hybridization, in particular hexagonal (h-BN) or rhombohedral (r-BN) polytypes. This is because they can be easily used as substrates for other 2D materials [1] or in flexible electronics [2]. Fabrication of such films using Metal-Organic Chemical Vapor Deposition (MOCVD) requires growth temperatures as high as possible in order to reach the transport-limited growth regime [3]. However, layers grown in the kinetic-limited regime also have interesting properties. BN layers grown at low temperatures exhibit a wide range of refractive index values [4]. Moreover, low growth temperatures allow for incorporating carbon atoms into BN films. This allows tuning the bandgap of the fabricated films in the range of 0.5-4.0 eV [5]. However, fabricating BN layers with very high carbon concentration remains a challenge. One of the key parameters in the growth of BN-based layers via MOCVD is the flow ratio of the nitrogen source (typically ammonia) to the boron source (typically triethylborane or trimethylborane) [4]. In this communication, we show that for layers grown at temperatures below 1200 ºC, we are able to switch between the growth of two kinds of layers with radically different optical and electrical properties by altering only the ammonia flow rate through the reactor chamber. For ammonia flow rates comparable to the triethylborane (TEB) flow, we were able to fabricate porous and transparent BN layers with low carbon concentrations and therefore high resistance values of MΩ or greater on a 1×1 cm2 sample. For ammonia flow rates in high excess (up to 50 times) of the TEB flow rates, we were able to fabricate nontransparent, highly absorptive layers with very high carbon concentration and resistance values in the range of single kΩ or less on a 1×1 cm2 sample. Moreover, these two types of layers exhibit radically different refractive index values. In the case of the transparent BN films, the effective refractive index values are lower than the refractive index of the bulk BN [6], while for the non-transparent films, the refractive index values are much higher. The causes of these differences as well as possible applications will also be discussed. This research was funded by the National Science Centre, grants no. 2019/33/B/ST5/02766 and 2020/39/D/ST7/02811. [1] K. Ludwiczak et al., ACS Appl. Mater. Interfaces 13, 47904 (2021) [2] J. Iwański et al., Acta Phys. Pol. 4, 139 (2021) [3] A. K. Dąbrowska et al., 2D Mater. 8, 015017 (2020) [4] K. Pakuła, et al., arXiv:1906.05319 (2019) [5] W. Xie et al., Journal of Carbon Research 2, 2 (2016) [6] A. Segura et al., Phys. Rev. Mater. 2, 024001 (2018)

Authors : Šarūnas Jankauskas, Andrius Vasiliauskas, Vitoldas Kopustinskas, Mindaugas Andrulevičius, Asta Guobienė, Brigita Abakevičienė, Šarūnas Meškinis
Affiliations : Institute of Materials Science, Kaunas University of Technology, Baršausko 59, Kaunas, Lithuania

Resume : INTRODUCTION Modern motion sensing solutions require encoders, devices that can ensure detection of small position variations and speed changes in different metrology instruments and other high precision machinery. Today, optical scales are considered to be one of the most accurate encoders, however it lacks versatility when operating near dew point, where fogging mechanism can hinder its applications due to signal disruption. To overcome such obstacle, optical transparency could be spared by developing an anti-fogging, scratch-resistant hydrophilic diamond-like carbon (DLC) films and nanocomposites. Therefore, in the present research, diamond-like nanocomposites containing SiOx and DLC carbon films doped by nitrogen were grown and studied. EXPERIMENTAL/THEORETICAL STUDY In this study, diamond-like nanocomposite film containing SiOx deposition was carried out using an anode layer ion source from the hexamethyldisiloxane vapor and hydrogen gas mixture. DLC films were doped by nitrogen and grown using two different methods. Those methods were graphite target reactive magnetron sputtering and inductively coupled plasma (ICP) plasma beam-assisted magnetron sputtering. For structure and morphology, investigations were carried out using Raman scattering spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). In addition, water contact angle of the samples was studied. RESULTS AND DISCUSSION In all cases, DLC films containing SiOx exhibited hydrophobic behavior, though post-treatment using oxygen plasma, allowed to reduce the wetting angle to 1o. This can be related to OH group formation on the surface of our samples. The growth dynamics of non-hydrogenated DLC films doped with nitrogen (DTAD: N) were studied in terms of nitrogen flow and time. When grown on the glass using 25 sccm nitrogen flow, the wetting angle of the DTAD:N films have decreased to 18o over the course of 10 min. duration of the measurement. These results were further explained from the chemical composition observations. No correlation between the contact angle, structure and roughness of our films was found. CONCLUSION In conclusion, hydrophobic behavior of fabricated DLC:SiOx films was changed to superhydrophilic, using oxygen plasma post-treatment. This was explained by the formation of -OH functional groups. Decreased contact angle was observed in hydrogen-free diamond-like carbon (DLC) films doped with nitrogen. Changes in chemical composition explain these observed results. ACKNOWLEDGMENTS This research was supported by the European Social Fund under the Measure 01.2.2-LMT-K-718 ‘Targeted Research in Smart Specialisation Areas’ (project No 01.2.2-LMT-K-718-03-0058).

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Session 3 - Epitaxy of low-dimensional materials: substrate/epilayer interactions, nanostructures-4 : F. Cheynis
Authors : Vera Marinova
Affiliations : Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, Sofia, Bulgaria

Resume : Recently, graphene and two-dimensional (2D) transition metal dichalcogenides (TMDCs with general formula MX2, where M represents transition metal and X represents chalcogen) open a great potential for direct integration with silicon (Si) technology, due to their outstanding chemical, physical, electronic, and optical properties. Here, we report the synthesis details of graphene and 2D layers using bottom-up techniques, their characterizations, and potential applications. In term of graphene, single and multilayers were synthesized using Chemical Vapour Deposition (CVD) method and transferred on varieties of rigid and flexible substrates, analyzed by Raman spectroscopy, optical and electrical measurements. For TMDCs layers (as PtSe2, WSe2) we used an atmospheric pressure thermally assisted conversion (TAC) method of pre-deposited by Magnetron Sputtering technique metal layers. The existence of 2D PtSe2 and WSe2 layers were confirmed using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analysis. In addition, Optical microscopy (OM) and atomic force microscopy (AFM) mapping of WSe2 revealed the formation of isolated flakes with different shapes, mainly concentrated near the substrate’s edges, which tended to form clusters and to further overlap to continuous layers. Performed photoluminescence measurements confirmed the existence of atomically thin flakes and 2H-WSe2 continuous layers. Spectroscopic ellipsometry were used to determine the thicknesses. Based on optical and electrical measurements, graphene and selected TMDCs nanolayers has been proposed as supporting conducive electrodes for tunable liquid crystal (LC) phase retarders. The functionality of the assembled LC devices was proved by electro-optical measurements such as threshold and saturation voltage and the phase retardation. Moreover, resistor-like behavior of PtSe2 and WSe2 layers suggested their unlimited prospects for integration into a variety of heterostructures. Acknowledgments The authors acknowledge the COST Action CA20116 “European Network for Innovative and Advanced Epitaxy”, OPERA. V. M. acknowledges the financial support by the European Regional Development Fund within the Operational Programme ‘Science and Education for Smart Growth 2014–2020’ under the Project CoE ‘National Center of Mechatronics and Clean Technologies’ BG05M2OP001-1.001-0008-C01 and Bulgarian Science Fund under the project number КП-06-Н-58/12.

Authors : Z. Konstantinovic1, V. Fuentes2, Ll. Balcells2, A. Pomar2 and B. Martinez2
Affiliations : 1 Center for Solid State Physics and New Materials, Institute of Physics Belgrade, University of Belgrade, Serbia; 2 Institut de Ciencia de Materials de Barcelona, ICMAB-CSIC, Campus UAB, 08193 Bellaterra, Spain.

Resume : Self-assembled Network of Nanostructures in Functional Oxide Thin Films Z. Konstantinovic1, V. Fuentes2, Ll. Balcells2, A. Pomar2 and B. Martinez2 1 Center for Solid State Physics and New Materials, Institute of Physics Belgrade, University of Belgrade, Serbia 2 Institut de Ciencia de Materials de Barcelona, ICMAB-CSIC, Campus UAB, 08193 Bellaterra, Spain. Complex oxide thin films are often elastically strained, due to film-substrate lattice mismatch, and this lattice strain can, in some cases, select preferential growth modes leading to the appearance of different self-organized nanostructured morphologies. This behaviour offers enormous potential for the implementation of new nanodevices while, at the same time, attracts great attention due to their rich physics. Among other complex oxides of interest, strongly correlated systems, such as manganese perovskites with colossal magnetoresistance and half metallic characteristics, environment friendly multiferroics and/or spin-orbit coupling perovskite, have emerged as promising candidates for miniature spintronic devices. In this work we report on the controlled fabrication of self-assembled networks of nanostructures in various functional oxide thin films. In highly epitaxial La2/3Sr1/3MnO3 thin films, all nano-objects form long-range ordered arrays running in the steps’ direction defined by the miscut angle of underlying substrate [1]. A very similar behavior is observed in multifferoic BiFeO3 thin films [2], as well as in SrIrO3 system that exhibits a strong spin-orbit coupling [3]. It is shown that when no structural relaxation exits, self-organization process is directly promoted by the topological features of the substrate. Common features of the spontaneous formation of self-organized nanostructure formation in various systems are summarized considering the impact of kinetic growth effects and the presence of the lattice strain. The influence of the presence of such regular ordered nanostructured arrays on the functional properties is also discussed. Finally, the growth of self-assembled nanoparticles on top of nanostructured antidots arrays is explored [4]. [1] Z. Konstantinović, J. Santiso, Ll. Balcells and B. Martínez, Small 5, 265 (2009) [2] B. Colson, V. Fuentes, Z. Konstantinović, D. Colson, A. Forget, N. Lazarević, M. Šćepanović, Z.V. Popović, C. Frontera, Ll. Balcells, B. Martínez, A. Pomar, Journal of Magn. Magn. Mat 509, 166898 (2020). [3] V. Fuentes, Z. Konstantinović, Ll. Balcells, B. Martínez and A. Pomar under preparation [4] Z. Konstantinović, F. Sandiumenge, J. Santiso, Ll. Balcells and B. Martínez, Nanoscale 5, 1001 (2013).

15:15 Coffee Break    
Session 4 - Physical properties of epitaxial materials, relationships between structure, materials chemistry and targeted physical properties-1 : P. Ferreira
Authors : D. Rusu1, J. J. P. Peters1, T. P. A. Hase1, S. D. Seddon1, R. Beanland1, M. Alexe1, A.M. Sanchez1*
Affiliations : Department of Physics, University of Warwick, Coventry, United Kingdom

Resume : The rapid improvement in materials growth and processing techniques has produced novel structures with unique functionalities. Electron microscopy plays a key role in understanding the structure of these novel materials and controlling them at an atomic level. The development of spherical aberration correctors for electromagnetic lenses established a major improvement in the new generation of electron microscopes. Using aberration-corrected scanning transmission electron microscopy (STEM), we analysed in detail the domain structure of PbTiO3/(La,Sr)MnO3 ferroelectric capacitors with ultra-thin active ferroelectric layers. Annular Bright Field (ABF) imaging was used to directly visualise both the heavy and light elements, measuring their relative displacement and dipole distribution, unit cell by unit cell. For a given system with a set lattice strain, the depolarization field becomes relatively large at smaller film thicknesses. The polarisation maps of different PbTiO3 thin films revealed a clear influence of the asymmetric screening of the depolarizing field on the equilibrium domain pattern. The dipole distribution reveals an evolution from conventional 180° Kittel-type domains to flux closure and vortex-type domain configurations with reduced film thickness. Additionally, effects such as polarisation and octahedral tilt suppression can be observed local to the interface. Supported by DFT calculations, we show how the different polarisation orientations interact with the LSMO at the interface. This provides insight into how such devices may be designed and tuned to achieve the desired performance. Additionally, ferroics can form vortices and skyrmions under particular boundary conditions. Here, we focus on the formation of modulated ferroelectric vortices in PbTiO3 sandwiched between two SrRuO3 electrodes on SrTiO3-buffered DyScO3 (110) substrate. The local structure is resolved using a combination of STEM and conventional TEM. Two orthogonal modulations were revealed. This incommensurate polar crystal may be an equivalent to the incommensurate spin crystals found in ferromagnetic materials. 1. Pantel, D., Goetze, S., Hesse, D. & Alexe, M. Reversible electrical switching of spin polarization in multiferroic tunnel junctions. Nat. Mater. 11, 289–293 (2012). 2. Stengel, M., Vanderbilt, D. & Spaldin, N. A. Enhancement of ferroelectricity at metal–oxide interfaces. Nat. Mater. 8, 392–397 (2009). 3. Peters, J. J. P., Apachitei, G., Beanland, R., Alexe, M. & Sanchez, A. M. Polarization curling and flux closures in multiferroic tunnel junctions. Nat. Commun. 7, 13484 (2016). 4. Rusu, D., Peters, J. J. P., Hase T. P. A., Gott J. A., Nisbet G.A.A., Strempfer J., Haskel D., Seddon S.D., Beanland R., Sanchez, A. M & Alexe M. Ferroelectric incommensurate spin crystals. Nature 602, 240–244 (2022)

Authors : E. Przeździecka1, A. Lysak1, A. Adhikari1, A. Wierzbicka1, P. Strąk2, P. Dłużewski1, R. Jakiela1, K. Zeinab1, P. Sybilski1
Affiliations : 1Polish Academy of Sciences, Institute of Physics, Al. Lotników 32/46, 02-668 Warsaw, Poland 2Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland

Resume : Recently, transparent conducting oxide (TCO) thin films have attracted considerable attention because of their simultaneously high transparency in the visible spectrum and low resistivity. In the TCO family II−VI oxides ternary alloys have attracted considerable interest of the scientific community due to the possibility of modulating their interesting optoelectronic properties. Direct bandgap of 2.5 eV in CdO is reported, whereas in case of MgO the energy gap of 7.8 eV is observed. Thus in (CdO-ZnO-MgO) oxide system we will able to control energy gap in a wide range from yellow to deep UV (UVC) region. Alternate growth of MgO, CdO and ZnO thin layers (quasi ternary alloys) can enhance advantages and reduce shortcomings of the individual oxide films (CdO and ZnO and MgO) and random alloys for particular new applications. Short period superlattices {CdO/MgO}n and {CdO/ZnO}n was grown by PA-MBE on different substrates. The good quality of crystals was confirmed by High Resolution X-ray Diffraction and Transmission Electron Microscopy (TEM) techniques. X-ray diffraction confirmed cubic structure of the samples in case of CdO/MgO SLs and cubic-hexagonal structures in case of CdO/ZnO SLs. Reciprocal space maps were collected to analyze the strain in the SLs layers with the very high precision. Local lattice parameter were measured by digital processing of experimental HRTEM images. From TEM and small angle X-ray measurements thicknesses the growth rates of individual layers of MgO and CdO and ZnO have been extracted. The thicknesses of the CdO, ZnO and MgO sublayers influence the measured band gap. The direct band gap of {CdO/MgO} superlattice were tuned from 2.6 eV to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by ab initio method still obtained data have the same trend. The presented CdO/ZnO short period superlattices have a good transparency and we are able to change the energy gap for this structures in the range from 2,68 to ~3,1 eV. This work shows that {CdO/MgO} and {CdO/ZnO} quasi alloys can be useful in developing new optoelectronic devices such as detectors for visible, and UV A, UV B and UV C region as well. This work was supported in part by the Polish National Science Center, Grants No. 2019/35/B/ST8/01937, and 2021/41/B/ST5/00216.

Authors : J.A. Mathew, A. Lysak, V. Tsiumra, R.Jakiela, A. Wierzbicka, E. Przezdziecka, M. Stachowicz, A. kozanecki
Affiliations : Institute of Physics Polish Academy of Sciences, Aleja lotników 32/46, Warszawa 02-668, Poland

Resume : In this work, we report the influence of Mg and Oxygen contents on the structural and luminescence properties of Eu doped ZnMgO layers. ZnMgO:Eu thin layers are deposited on a-Al2O3 substrates by oxygen plasma assisted molecular beam epitaxy. The samples are grown at 550°C under two different experimental conditions; i) varying Mg fluxes from sample to sample while keeping the oxygen flow constant; ii) varying the oxygen flow while keeping all other parameters constant. EDX measurements are carried out to determine specific elemental composition. Compositional depth profiling is performed using Secondary Ion Mass spectrometry. Structural investigations are carried out using XRD and SEM techniques. Both magnesium and oxygen is found to have crucial impact on the luminescence properties of Europium as seen from the photoluminescence and cathodoluminescence analysis.

Authors : S. Gonzalez(a*), I. C. Infante(a), B. Vilquin(a), P. Rojo-Romeo(a), S. Brottet(a), G. Herrera(b), C. Raton(b), A. Reyes(b), O. Boisron(b), F. Tournus(b), D. LeRoy(b), V. Dupuis(b), M. Bugnet(c), X. Weng(d), L. Martinelli(d), G. Renaud(e), A. Resta(f), A. Vlad(f), A. Coati(f), P. Schöffmann(f), E. Otero(f), P. Ohresser(f)
Affiliations : a. Univ Lyon, CNRS, ECL, INSA Lyon, UCBL, CPE, INL, UMR 5270, 69621 Villeurbanne, France ; b. Institut Lumière Matière, UMR 5306, CNRS Université Claude Bernard Lyon 1, France; c. Univ Lyon, CNRS, INSA Lyon, UCBL, MATEIS, UMR 5510, 69621 Villeurbanne, France; d. European Synchrotron Radiation Facility, 38000 Grenoble, France; e. Université Grenoble Alpes, CEA, INAC, MEM, 38000 Grenoble, France; f. Synchrotron SOLEIL, CNRS-CEA, L’Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette, France

Resume : Nanomultiferroic composites are promising systems where the interfacial coupling between different ferroics can be driven by magnetic, voltage and strain mediation approaches to explore new technological applications [1]. Bulk FeRh alloy chemically ordered in the CsCl-type B2 phase, is characterized by a remarkable magneto-structural transition close to room temperature (~350 K) from an anti-ferromagnetic phase to a ferromagnetic one. Remarkably, we previously showed that in nanocrystallites (NC) as small as 5 nm, B2 phase is attainable through UHV high-temperature annealing, but depicts high magnetization down to 3 K [2], confirming the stabilization of intrinsic ferromagnetism in B2 FeRh NCs. Moreover as in nanoscale systems, the magnetic order of FeRh is very sensitive to interfaces, strain and surface terminations [2, 3], we have deposited such NCs on perovskite oxides substrates. Here, we focus on studying ultimately small nanomultiferroic systems (3 to 7nm FeRh NCs) on perovskite oxides, SrTiO3 (001) crystals (STO) and BaTiO3 (BTO) thin films. Material choices are based on structural compatibility, in a goal of using the coupling of strain and magnetic order to obtain voltage control over metamagnetic FeRh transition, as this was previously observed in hybrid multiferroic: 22 nm-thick FeRh film on BTO crystal [4]. We show that randomly deposited particles on BTO or STO adopt specific orientations after annealing. In addition to the usual epitaxy relationship [100]FeRh//[110]STO & [001]FeRh//[001]STO as expected for thin films, another orientation (45° rotation) has been observed, together with more complex geometries (particles lying on a {110} facet). For the later, a coincidence between {211}FeRh and {130}STO seems to be the driving force, and results in “satellite peaks” in some FeRh rings, around the main orientations. Nevertheless, important questions need to be discussed, such as the effects of reduction on the nanostructure. Indeed, we have observed that unprotected FeRh particles, which are then oxidized, can be reduced by UHV annealing, which can explain why epitaxy had been observed for annealed particles that subsequently appeared to be (partially) oxidized with XAS measurements at room or low temperature. Ref: [1] W. Eerenstein, N.D. Mathur, J.F. Scott, Nature, 442, pp. 759-765 (2006); N. A. Spaldin and R. Ramesh, Nature Mater.18, 203 (2019) [2] A. Hillion et al., Phys. Rev. Lett. 110, 087207 (2013) ; V. Dupuis et al. Beilstein J. Nanotechnol. 7, 1850 (2016) [3] Liu et al., Euro. Phys. Lett. 116, 27006 (2016) ; Lewis et al., J. Phys. D 49, 323002 (2016) [4] Cherifi et al., Nature Mater. 13 (2014) 345 ; Liu et al., Nature Comm. 7 (2016)

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Session 4 - Physical properties of epitaxial materials, relationships between structure, materials chemistry and targeted physical properties-2 : A. Sanchez
Authors : Paula Ferreira, Alichandra Castro, Paula M. Vilarinho
Affiliations : Department of Materials and Ceramic Engineering, CICECO – Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal

Resume : Ferroic materials may find application in several fields including ultrafast data reading, enhanced storage capacity, laser-assisted electronic data recording in ferroelectric memories, catalytic materials, and sensor devices. Nanopatterning metal oxides using sustainable methodologies may be a way to modify the properties of metal oxide thin films. In this work, it will be presented several examples in which the ordered thin layers were prepared with fine control of the porous structure and great homogeneity. Nanoporous thin films of lead titanate [1,2] and bismuth ferrite [3], as examples of oxides with perovskite and ferrite structures, were prepared by block-copolymer self-assembly (Figure 1). Films with different thicknesses and pore organizations were also prepared. The films were characterized in relation to the structure and morphology by X-rays diffraction, scanning electron microscopy and atomic force microscopy. The electric properties were measured at nanoscale by piezoelectric-response force microscopy and are compared with dense counterparts with similar thickness. Nanopatterned PbTiO3 films present higher switchable polarization and (d33)eff piezoelectric coefficient than dense thin films (137.6 ± 6.7 pm/V and 49.6 ± 0.7 pm/V versus 85.1±2.0 pm/V and 35.7±0.8 pm/V, respectively), demonstrating the positive effect of porosity on the enhancement of the ferroelectric properties. Nanopatterned BiFeO3 layers with 66 nm of thickness and average pore diameter of 100 nm at 600 °C were prepared. The large vertical porosity markedly enhances the local electric and macroscopic magnetic properties when compared with the dense counterparts. The vertical porosity orients the piezoelectric domains and reduces the energy necessary to reorient the dipoles. The induced instability in the dipole-dipole interactions results in the increase of the effective piezoelectric coefficient. [1] A. Castro, P. Ferreira, B. J. Rodriguez; P.M. Vilarinho, J. Mater. Chem. C (2015) 3, 1035–1043. [2] A. Castro, P. Ferreira, P.M. Vilarinho, J. Phys. Chem. C (2016) 120, 10961−10967. [3] A. Castro, M.A. Martins, L.P. Ferreira, M. Godinho, P.M. Vilarinho, P. Ferreira, J. Mater. Chem. C, (2019) 7, 7788-7797. Acknowledgement This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC). NANOTRONICS (IF/300/2015), FLEXIDEVICE (PTDC/CTM-CTM/29671/2017) and Cost action OPERA CA 20116 are also thanked.

Authors : Cinthia Piamonteze 1, Anna Zakharova 1, Marco Caputo 1, Eduardo Bonini Guedes 1, Francis Bern 2, S. R. V. Avula 1, M. Studniarek 1, C. Autieri 3, M. Ziese 2, M. Radovic 1, F. Nolting 1 and I. Lindfors-Vrejoiu 4
Affiliations : 1 Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland; 2 Felix-Bloch-Institut fuer Festkoerperphysik, Universitaet Leipzig, Leipzig, Germany; 3 International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland; 4 II. Physikalisches Institut, Universitaet zu Koeln, Koeln, Germany

Resume : Optimally doped manganites (La0.7A0.3MnO3 (A=Ca, Sr, Ba)) is one of the most investigated correlated oxides due to its interesting properties: ferromagnetic metal with high spin polarization, ordering above room temperature (in bulk), colossal magnetoresistance [1,2]. However, the finding of a magnetic dead layer [3] has partially hindered its further exploration in devices, since La0.7A0.3MnO3 becomes non-ferromagnetic and insulating typically below thicknesses of 5-unit cells (uc) [4]. Here, we present our results using x-ray magnetic circular dichroism (XMCD) and x-ray linear dichroism (XLD) on optimally doped manganites interfaced with SrRuO3 (SRO) where we show that the magnetic dead layer can be hindered by the addition of this interfacial layer [5,6]. We show that 1 uc La0.7Ba0.3MnO3 (LBMO) inserted between two layers of SRO, 3uc-thick each, is ferromagnetic up to 130K. The XMCD shows clear Mn remanence at this temperature. Element-specific magnetization curves evidence the antiferromagnetic coupling between Mn and Ru. DFT calculations show that due to the SRO buffer layer, LSMO preserves the octahedral rotations from bulk. [5] Further, we investigated different thicknesses of La0.7Sr0.3MnO3 (LSMO) grown on SrTiO3 (STO) compared to LSMO/SRO bilayers on STO [6]. The orbital occupation of Mn in these two interfaces has been quantified by XLD. We observe that the Mn orbital occupation in the interface with SRO or STO is different, as previously predicted by DFT [7]. However, in the ultra-thin limit the interfaces have similar orbital occupation. We also observe that the Mn valence is different in these two interfaces. Our work shows that the magnetically stability of 1-2uc-thick LSMO when interfaced with SRO can be attributed to multiple factors. From one point of view, the overlap of Mn and Sr bands at LSMO/SRO interface, shown by DFT, leads to a 3D electronic structure, hindering quantum confinement. Further the SRO interlayer provides a buffer allowing the bulk MnO6 octahedral rotations and the preservation of the bulk Mn valence. [1] J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, R. Ramesh and T. Venkatesan. Nature 392, 794–796 (1998). [2] Y. Tokura, Critical features of colossal magnetoresistive manganites. Rep. Prog. Phys. 69, 797 (2006). [3] M. Bibes, S. Valencia, Ll. Balcells, B. Martınez, J. Fontcuberta, M. Wojcik, S. Nadolski, and E. Jedryka. Phys. Rev. B 66, 167 (2002). [4] M. Huijben, L. W. Martin, Y.-H. Chu, M. B. Holcomb, P. Yu, G. Rijnders, D. H. A. Blank, and R. Ramesh. Phys. Rev. B 78, 094413 (2008). [5] C. Piamonteze, F. Bern, S. R. V. Avula, M. Studniarek, C. Autieri, M. Ziese, and I. Lindfors-Vrejoiu. Appl. Phys. Lett. 118, 152408 (2021). [6] A. Zakharova , M. Caputo, E. B. Guedes , M. Radovic, F. Nolting , and C. Piamonteze. Phys. Rev. Mater. 5, 124404 (2021). [7] Lv, K., Zhu, H. P., Zou, W. Q., Zhang, F. M. & Wu, X. S. J. Appl. Phys. 117, 185305 (2015).

Authors : Tamara Potlog1, Ion Lungu1, Lidia Ghimpu2
Affiliations : 1Physics Department and Engineering, Moldova State University 2 Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, Chisinau, Moldova

Resume : Recent, the II-VI wide band gap semiconductors have application in a variety of solid-state electronic devices, such as light emitting diodes (LED), photosensors, thin-film transistors and solar cells. Several of the wide band gap II-VI compounds have been prepared with good n-type conductivity, the only compound which has shown low enough resistivity in p-type form to be useful in p-n junction devices is ZnTe. From the standpoint of the crystal lattice mismatch (0.216 Å), the n-type CdS and p-type ZnTe thin films present a suitable combination to create a heterojunction (HJ). ZnTe-CdS epitaxial HJs have been prepared by close space sublimation (CSS) method by consequently deposition of CdS and ZnTe films on ZnO/glass substrates. ZnO thin films were deposited by DC magnetron sputtering using ZnO:Ga:Cl ceramic targets. The effect of deposition temperature, film thickness and Ga and Cl concentrations on the electrical properties of ZnO thin films will be discussed herein. From the Hall measurements using the van der Pauw method, the resistivity value of 1.5 × 10− 4 Ω⋅cm, an average transparency of about 90%, mobility of 25 cm2/Vs were estimated for optimized ZnO:Ga thin films with a thickness of 400 nm. Also, the crystalline structure of each component of the ZnO/CdS/ZnTe heterostructure studied by x-ray diffractometer with CuKα radiation (λ = 0.15406 nm will be discussed. The optical properties measured with the Cary 60 UV-Vis spectrophotometer, such as film absorption coefficient and optical band gap in the range 300–1000 nm will be analyzed. The current–voltage (I–V) and capacitance–voltage (C–V) measurements were conducted using a Keithley 2400, a solar simulator (AM1.5, 100 mW/cm2) and Labtracer software. We optimized the photoelectrical parameters of ZnO/CdS/ZnTe HJs in function of ZnTe films substrate and source temperatures. Next, for optimized ZnO/CdS/ZnTe HJ with open circuit voltage 0.65 V, short circuit current densities of about 12 mA/cm2, electrical data were recorded in the (270-400) K temperature interval, dark. The forward current transport mechanism is discussed. Field for improving the photovoltaic performance of the ZnO/CdS/ZnTe HJs could be intermediate band solar cells.

Authors : Karolina Pietak [1,2], Jakub Jagiello [1], Artur Dobrowolski [1], Tymoteusz Ciuk [1]
Affiliations : [1] Łukasiewicz Research Network – Institute of Microelectronics and Photonics, Al. Lotnikow 32/46, 02-668 Warsaw, Poland [2] Faculty of Chemistry, Warsaw University of Technology, ul. Noakowskiego 3, 00-664 Warsaw, Poland

Resume : Enhancement of the Raman signal intensity is currently among the most researched directions in developing Raman-based characterization techniques of all 2D materials as it elevates detection limits of their fine structural properties. The interest in Raman signal intensification is also triggered by the wide range of applications it can benefit, such as biochemistry and biosensing, polymer and materials science, catalysis, electrochemistry, the study of high-temperature processes, and the detection of hazardous gases [1]. In this work, we demonstrate a method for the enhancement of Raman active modes of hydrogen-intercalated [2] quasi-free-standing epitaxial chemical vapor deposition graphene and the underlying semi-insulating 6H–SiC(0001) substrate through constructive signal interference within atomic-layer-deposited amorphous Al2O3 passivation. We find that an optimum Al2O3 thickness of 85 nm for the graphene 2D mode and one of 82 nm for the SiC longitudinal optical A1 mode at 964 cm–1 enable a 60% increase in their spectra intensities. We demonstrate the method’s efficiency in Raman-based determination of the dielectric thickness and high-resolution topographic imaging of a graphene surface [1,3]. The research leading to these results has received funding from the Research Foundation Flanders (FWO) under Grant No. EOS 30467715, the National Science Centre under Grant Agreement No. OPUS 2019/33/B/ST3/02677 for project “Influence of the silicon carbide and the dielectric passivation defect structure on high-temperature electrical properties of epitaxial graphene,” and the National Centre for Research and Development under Grant Agreement No. LIDER 0168/L-8/2016 for the project “Graphene on silicon carbide devices for magnetic field detection in extreme temperature conditions.” Karolina Piętak acknowledges financial support from the IDUB project (Scholarship Plus programme). [1] K. Piętak, J. Jagiełło, A. Dobrowolski, R. Budzich, A. Wysmołek, T. Ciuk, Enhancement of graphene-related and substrate-related Raman modes through dielectric layer deposition, Applied Physics Letters, 120, 063105 (2022). [2] M. Szary, S. El-Ahmar, T. Ciuk, The impact of partial H intercalation on the quasi-free-standing properties of graphene on SiC(0001), Applied Surface Science, 541, 158668 (2020). [3] A. Dobrowolski, J. Jagiełło, D. Czolak, T. Ciuk, Determining the number of graphene layers based on Raman response of the SiC substrate, Physica E: Low-dimensional Systems and Nanostructures, 134, 114853 (2021).

Authors : Lucian Pintilie, Cristina Chirila, Luminita Hrib, Georgia Boni, Iuliana Pasuk, Cristian Radu, Cosmin Istrate, Lucian Trupina, Ioana Pintilie
Affiliations : National Institute of Materials Physics, Magurele, Romania

Resume : Properties of undoped and doped epitaxial PZT films will be reviewed. It will be shown that trace impurities from the target can have a significant impact on the macroscopic electrical properties. It will be also shown that low level doping with Nb and Fe can induce changes in the direction of the ferroelectric polarization in the as-grown films, upward in Nb doped films (assumed as n-type doping), and downward in Fe doped films (assumed as p-type doping). p-n homojonction were also grown, with current-voltage characteristics suggesting a resistive behavior. At the end, considerations on the polarization switching in epitaxial films will be made, supporting homogeneous switching triggered by charge injection at the electrode interfaces.

10:30 Coffee Break    
Session 5 - Applications-oriented epitaxy: device architecture, doping, localized epitaxy & Advanced epitaxial materials for technological transfers-1 : A. Sawicka
Authors : R.Vermeersch,G.Jacopin,B.Gayral,J.Pernot,B.Daudin
Affiliations : Univ. Grenoble Alpes, CEA, IRIG-PHELIQS, NPSC, 17 rue des martyrs, 38000 Grenoble, France; Univ. Grenoble Alpes, Grenoble INP, CNRS, Institut Néel, 38000 Grenoble, France; Univ. Grenoble Alpes, CEA, IRIG-PHELIQS, NPSC, 17 rue des martyrs, 38000 Grenoble, France; Univ. Grenoble Alpes, Grenoble INP, CNRS, Institut Néel, 38000 Grenoble, France; Univ. Grenoble Alpes, CEA, IRIG-PHELIQS, NPSC, 17 rue des martyrs, 38000 Grenoble, France

Resume : In spite of a continuous interest in AlGaN based deep-UV emitters in view of various applications, these devices are still exhibiting an insufficient efficiency, which prevents them from being widely used. Discarding the dislocation density, which is not a drastic limitation if below 108 cm-2, the limitation of layer-based deep-UV LEDs primarily relies on low light extraction efficiency and difficult electrical injection. Due to their unique geometry, AlGaN nanowires (NWs) are promising to address those issues: the absence of extended defects, as well as the morphology of nitride NWs, are favorable to improve the dopant incorporation and light extraction. As a matter of fact, some of us recently reported axial pn-junction realization with Mg acceptors in the p-region and Si donors in the n-region [1]. Furthermore, the stabilization of Si in shallow state in AlN NWs was recently demonstrated [2]. In this work, we review the realization of AlN NW based light emitting diodes grown by plasma-assisted molecular beam epitaxy. For both n-type and p-type NW sections as well as for active region, the use of binary AlN allows one to overcome the spontaneous formation of AlN/GaN superlattice-like structure of AlGaN and concomitant alloy inhomogeneities making difficult the control of active region composition and emission wavelength [3]. By contrast, the use of short period AlN/GaN superlattices in the active region is one key to reach deeper UV, between 210 and 240 nm. Current voltage (I-V) measurements of the device show a rectifying behavior typical of pn junction assessing the effective n-type and p-type doping of the AlN sections. Electron beam induced current (EBIC) was used to identify the position of the space-charge region induced by the pn-junction within the NW, which was compared to the location of the cathodoluminescence (CL) signal. The correlation between EBIC and CL assesses the spatial superposition of both electric field and emitting area, a prerequisite to ensure light emission from electrical injection. Finally, electroluminescence (EL) spectra were acquired, exhibiting a peak at 285 nm, in agreement with the CL signal. The peak intensity follows the standard behavior of a diode, i.e. a linear increase of the optical power with current, before dropping. Various active area designs for wideband emission will be discussed in order to match DNA absorption band in view of sanitization applications. [1] A.-M. Siladie et al, Nano Lett. 19, 8357-8364 (2019) [2] R. Vermeersch et al., Appl. Phys. Lett. 119, 262105 (2021) [3] A. Pierret et al, M. Belloeil et al, Nano Lett. 16, 960−966 (2016)

Authors : Andrea Zelioli1, Arnas Pukinskas1, Algirdas Jasinskas1, Simona Pūkienė1, Silvija Keraitytė1, 2, Arnas Naujokaitis1, Martynas Skapas1, Monika Jokubauskaitė1, Evelina Dudutienė1, Artūras Suchodolskis1, Bronislovas Čechavičius1 and Renata Butkutė1, 2
Affiliations : 1 Center for Physical Sciences and Technology, Vilnius, Lithuania 2 Institute of Photonics and Nanotechnology, Faculty of Physics, Vilnius University, Lithuania

Resume : Several types of lasers, such as, solid-state, semiconductor, gas, excimer, and dye lasers, have been developed. Today lasers are used in many fields, particularly in optical fiber communication, optical digital recording, material processing, biology and medicine, spectroscopy, imaging, entertainment, and many others. Due to exceptional material properties and/or investigation conditions various application require unique set of laser parameters - emission wavelength, its tunability, beam quality, operation temperature, optical output power, as well as convenient method of laser excitation, power consumption, high-speed modulation and device size is very important. Vertical-external-cavity surface-emitting lasers (VECSEL) also called optically pumped semiconductor lasers (OPSL) or semiconductor disk laser (SDL) belong to relatively new laser family that combines many of the desirable properties. VECSELs were developed to overcome key problems typical to conventional semiconductor lasers. In comparison to both types of electrically pumped Vertical-cavity surface-emitting lasers (VCSELs), which emit circular fundamental transverse mode beam but exhibit low power and edge emitting lasers (Fabry-Perot and DFB) that can reach high output power but an asymmetric beam with strong angular divergence, VECSELS are capable to generate high optical power with circular beam quality. In this work the main activity was focused to investigation of the technological parameters required to grow high quality GaAsBi quantum structures, balance the strain during the growth procedure, obtain sharp interfaces and investigate photoluminescence properties. Multiple quantum well structures were grown using solid-source MBE system (Veeco GENxplor R&D) equipped with standard cells for metallic Al, Ga, Bi and unique As design source generating arsenic dimers flux. Semi-insulating GaAs substrate oriented in (001) crystalline plane was selected as substrate. During this work the thickness of the quantum wells has been kept constant. Two different types of design were investigated, one consisting of two GaAsBi quantum wells with AlGaAs parabolic barriers and one with three rectangular GaAsBi/GaAs quantum wells encapsulated into AlGaAs parabolic barriers. To obtain high crystalline quality and enhanced optical properties of MQW structures the temperature of the substrate was varied from 420°C to 425°C, the beam equivalent pressure ratios of Bi/Ga and As/Ga were changed in the ranges of 1.05-1.10 and 0.4-3.0, respectively. The HR-TEM and STEM investigation evidenced that GaAsBi QWs with AlGaAs PQBs were formed successfully. Photoluminescence measurements determined the relationship between growth conditions and emission energy and intensity and highlighted the crucial growth parameters - As/Ga beam equivalent pressure ratio, Bi flux, growth rate and substrate temperature.

Authors : Virginia Falcone(1), Andrea Ballabio(1), Andrea Barzaghi(1), Carlo Zucchetti(1), Luca Anzi(1), Federico Bottegoni(1), Jacopo Frigerio(1), Roman Sordan(1), Paolo Biagioni(2) and Giovanni Isella(1).
Affiliations : 1.LNESS Dipartimento di Fisica, Politecnico di Milano, Via Anzani 42, I-22100 Como, Italy 2.Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano, Italy

Resume : The direct epitaxial growth of silicon and germanium on silicon (Ge-on-Si) has fostered the development of visible - near-infrared detectors. A viable route to enhance the responsivity of these photodetectors might be exploiting the micro-structuring of the absorbing layer to increase the effective volume of interaction between light and matter. In this work we report on a new type of detectors, obtained from Si and Ge micro-crystals epitaxially grown on a patterned Si substrate [1,2]. The faceted morphology and relatively high aspect ratio of the microcrystals is seen to enhance the fraction of absorbed light and the detector responsivity in the wavelength region of the indirect regime of absorption, as compared to conventional planar devices. Modeling of the visible - near-IR absorption properties of the Si and GeonSi micro-crystals has been performed by finite difference time (FDTD) simulations [3,4]. This confirms that crystal faceting and pattern periodicity lead to enhanced light absorption as compared to conventional epitaxial layers and makes Si-Ge micro-crystals promising building blocks for optoelectronic devices operating in the VIS- NIR spectral region. A first step of electrical and optical characterization was made by means of a manipulator with a tip of 100 nm, enableing the electrical contact of a single microcrystal. The IV curves confirmed the pin doping profile inside the microcrystals, and its optimization by the implantation of the final p-doped top layer. The responsivity of the single microcrystal proved the VIS -NIR photoresponse. The main challenge in realizing vertically illu-minated photodiodes based on microcrystals is the formation of a top transparent contact that can adapt to the surface morphology and bridge the 100-200 nm gap between adjacent microcrystals. To this purpose, graphene can be used as a suspended continuous top contact. The Ge microcrystals fabricated devices have been characterized by electrical and optical measurements that confirm the near-IR photoresponse [4]. Responsivity measurements experimentally confirm the enhanced absorption close to the germanium indirect gap. This responsivity enhancement is linked to light-trapping effects taking place within the micro-crystal array. 1. C. V. Falub et al., Scaling Hetero-Epitaxy from Layers to Three-Dimensional Crystals, Science, vol. 335, no. 6074, doi: 10.1126/science.1217666. 2. R. Bergamaschini et al., Self-aligned Ge and SiGe three-dimensional epitaxy on dense Si pillar arrays, Surf. Sci. Rep., vol. 68, no. 3–4, 2013, doi: 10.1016/j.surfrep.2013.10.002. 3. J. Pedrini et al., Broadband control of the optical properties of semiconductors through site-controlled self-assembly of mi-crocrystals, Opt. Express, vol. 28, no. 17, doi: 10.1364/OE.398098. 4. V. Falcone, et al., Graphene/Ge microcrystal photodetectors with enhanced infrared responsivity, APL Photonics,

Authors : Arkadiusz Ciesielski, Jakub Iwański, Piotr Wróbel, Rafał Bożek, Aleksandra K. Dąbrowska, Sławomir Kret, Jakub Turczyński, Johannes Binder, Krzysztof P. Korona, Roman Stępniewski, Andrzej Wysmołek
Affiliations : Arkadiusz Ciesielski; Jakub Iwański; Piotr Wróbel; Rafał Bożek; Aleksandra K. Dąbrowska; Johannes Binder; Krzysztof P. Korona; Roman Stępniewski, Andrzej Wysmołek - University of Warsaw, Faculty of Physics, Pasteura 5, 02-093 Warsaw, Poland Sławomir Kret; Jakub Turczyński - Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland

Resume : Distributed Bragg Reflectors (DBRs) are commonly used in optoelectronic devices which require an optical cavity, like lasers or diodes. In DBRs, layers with high and low values of refractive index are deposited alternately on top of each other. Such a structure allows for achieving almost 100% reflectance value for a wavelength range dependent on the refractive index contrast between the two types of layers as well as their thicknesses [1]. Although epitaxial techniques such as Metal-Organic Chemical Vapor Deposition (MOCVD) have been used to fabricate DBR structures for more than three decades, utilizing Boron Nitride (BN) to achieve this is a relatively new idea [2,3]. Commonly, the difference in the refractive index values between the two component layers of the DBR is a result of the use of two different materials or at least different amounts of specific elements in ternary or quaternary compounds. Additionally, the refractive index contrast may also be achieved by introducing porosity to at least one component layer [4,5]. In this communication, we show the fabrication and optical performance of DBRs in which both component layers are made of BN, but exhibit varying levels of porosity and therefore have different values of the refractive index. We are able to achieve this by manipulating only the temperature during the growth of the sample [6]. In contrast to the case of DBRs made of GaN or AlGaN [4,5], the fabrication of the whole structure is possible in a single MOCVD process, without the need for any post-process etching. For DBRs consisting of 15.5 layer pairs, we were able to achieve a peak reflectance reaching 90% [6], the position of which can be easily tuned in the visible and infrared parts of the electromagnetic spectrum. We also show that the fabricated DBRs can be easily utilized in the construction of optical microcavities. This research was funded by the National Science Centre, grants no. 2019/33/B/ST5/02766 and 2020/39/D/ST7/02811. [1] P. Yeh, Optical Waves in Layered Media, John Wiley & Sons: New York, 2005. [2] Q. Li et al., Opt. Mater. Express 11, 180-188 (2021) [3] F. AlQatari et al., Mater. Res. Express 8, 086202 (2021) [4] F. H. Fan et al., Sci. Rep. 7, 4968 (2017) [5] Y. Tian et al., Materials 15, 3536 (2022) [6] A. Ciesielski et al., arXiv:2206.02168 (2022)

12:15 Lunch Break    
Session 5 - Applications-oriented epitaxy: device architecture, doping, localized epitaxy & Advanced epitaxial materials for technological transfers-2 : B. Daudin
Authors : Marta Sawicka, Natalia Fiuczek, Grzegorz Muziol, Mateusz Hajdel, Marcin Siekacz, Anna Feduniewicz-Żmuda, Krzesimir Nowakowski-Szkudlarek, Henryk Turski, Mikołaj Żak, Oliwia Bilska, John J. Kelly, and Czesław Skierbiszewski
Affiliations : Institute of High Pressure Physics Polish Academy of Sciences “Unipress”, Sokołowska 29/27, 01-142 Warsaw, Poland Condensed Matter and Interfaces, Debye Institute for NanoMaterials Science, University of Utrecht, Princetonplein 1, Utrecht, the Netherlands

Resume : Electrochemical etching (ECE) has recently emerged as a very useful method to fabricate porous GaN of a decreased refractive index (1) or for removal of sacrificial layers and structure lift-off (2). Due to high selectivity against n-type doping, ECE technique can also serve as a tool to detect inhomogeneity in Si doping in GaN grown by molecular beam epitaxy (3). We demonstrate that the lateral growth rate of atomic steps during epitaxy of GaN:Si in metal rich conditions impacts local Si incorporation and we can resolve morphology-induced differences of Si doping within the layers using ECE. Most of the reports focus on ECE of n-type GaN for which the process is well controlled and wide range of porosities can be easily obtained. In this report we show the first controlled ECE of p-type GaN with a tunnel junction used for effective carrier injection (4). As a consequence of different band-bending at the at the semiconductor-electrolyte interface in case of n-type and p-type, the etching conditions are different. Threshold etching bias is lower for p-type and complete material removal could be obtained easier than for n-type of similar doping. In the last part of the talk, applications of porous GaN in device structures will be shown with particular focus on edge emitting laser diodes (LDs) (5). Porous GaN is used here as a material of lower refractive index in the bottom cladding. We disclose the process-flow we used to implement porous layer in a laser structure. We show optical and electrical characteristics of LDs with porous claddings. Porous LDs show surprisingly low slope efficiencies (0.2 W/A), relatively high threshold current densities (9.2kA/cm2) and blue-shifted emission (448.7 nm) when compared to standard LDs. Finally, we list the reasons of high losses and discuss possible routes for improvements. Acknowledgements: This work received funding from the Foundation for Polish Science (POIR.04.04.00-00-4463/17-00 and POIR.04.04.00-00-210C/16-00) and from National Science Centre Poland (2019/35/D/ST5/02950, 2019/35/D/ST3/03008 and 2019/35/N/ST7/02968). The research leading to these results has also received funding from the Norway Grants 2014-2021 via the National Centre for Research and Development grant no. NOR/SGS/BANANO/0164/2020. 1. C. Zhang et al., New Directions in GaN Photonics Enabled by Electrochemical Processes. ECS Transactions 72, 47-56 (2016). 2. S. H. Park et al., Wide bandgap III-nitride nanomembranes for optoelectronic applications. Nano Lett 14, 4293-4298 (2014). 3. M. Sawicka et al., Revealing inhomogeneous Si incorporation into GaN at the nanometer scale by electrochemical etching. Nanoscale 12, 6137-6143 (2020). 4. N. Fiuczek et al., Electrochemical etching of p-type GaN using a tunnel junction for efficient hole injection. Acta Materialia 234, 118018 (2022). 5. M. Sawicka et al., Electrically pumped blue laser diodes with nanoporous bottom cladding. Optics Express 30, 10709-10722 (2022).

Authors : N. Kilinc1, M. Erkovan2,3,* and S. Cardoso2
Affiliations : 1Department of Physics, Faculty of Science & Arts, Inonu University, Malatya, Turkey; 2Instituto de Engenharia de Sistemas E Computadores ? Microsistemas e Nanotecnologias (INESC MN), Lisboa, Portugal; 3Department of Computer Engineering, Beykoz University, Istanbul, Turkey

Resume : The use of hydrogen (H2) as a clean, efficient, and sustainable energy source has been expanding into various fields since it will permit the reduction of the CO2 gas generated by the combustion of fossil fuels. H2 is the smallest molecule, colorless, odourless, tasteless, and is a flammable gas, and it cannot be detected by human senses, unless it is present in high concentrations. In this regard, rapid and accurate H2 gas measurement is essential to alert to the formation of potentially explosive mixtures with air, to help prevent the risk of an unexpected explosion. In the present work, ultrathin platinum-gadolinium PtxGd1-x (x=1, 0.75, 0.5 and 0.25) alloy films are fabricated using co-sputtering with approximately 2nm in thickness onto SiO2/Si substrate. The stoichiometry, structural and electrical resistivity characterization of the films are obtained from EDX, RBS and XPS measurements. The structural characterization of ultrathin PtGd films showed smooth coverage of the surface, in a fcc crystalline plane (111). The resistive properties of the films are tested towards a hydrogen gas sensor between 25 °C ? 150 °C in the gas concentration ranging from 0.5% to 5%. The surface scattering phenomenon could explain the hydrogen gas sensing mechanism of ultrathin PtGd alloy thin films. It will discuss the effect of alloy composition, temperature and hydrogen concentration on the gas sensing properties of PtGd thin films. Acknowledgment: This study was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with a project number of 121M681.

Authors : L. G. Enger1, S. Flament1, O. Rousseau1, I. N. Bhatti1, B. Guillet1, M. Lam Chok Sing1, V. Pierron1, S. Lebargy1, J.M. Diez2, A. Vera2, I. Martinez2, R. Guerrero2, L. Perez2,3, P. Perna2, J. Camarero2, R. Miranda2, M. T. Gonzalez2, L. Méchin1
Affiliations : 1. Normandie Univ, UNICAEN, ENSICAEN, CNRS, GREYC, 14000 Caen, France; 2. IMDEA Nanociencia, Campus de Cantoblanco, 28049 Madrid, Spain; 3. Dept. Fisica de Materiales - Universidad Complutense de Madrid, Av. Complutense s/n 28040 Madrid, Spain

Resume : The detectivity of a magnetic sensor is defined as the ratio of its intrinsic noise to its sensitivity. We previously demonstrated that very low levels of low frequency noise can be achieved in high epitaxial quality La2/3Sr1/3MnO3 (LSMO) thin films [1]. Since LSMO is a room temperature ferromagnetic metal with Curie temperature around 360K, it is a good candidate for the realization of anisotropic magnetoresistive sensors operated at room temperature, even if they do not reach same sensitivity values as other spintronic sensors such as Giant Magnetoresistances (GMR) or Tunnel Magnetoresistances (TMR). Anisotropic Magnetoresistance (AMR) depends on the angle between the direction of the electrical current and that of the magnetization. It is therefore important to control the magnetic anisotropy in LSMO thin films, and in particular to achieve an uniaxial magnetic anisotropy, with a relatively low anisotropy field, named Ha, while keeping a very low electrical noise. We will present results obtained with AMR sensors patterned in 30 to 60 nm thick epitaxial La2/3Sr1/3MnO3 (LSMO) thin films, deposited on 4°, 6° or 8° vicinal SrTiO3 (STO) substrates by pulsed laser deposition. The use of a vicinal substrate, which presents a surface miscut angle regarding to the crystallographic plane, was used to induce uniaxial anisotropy with an easy magnetic axis along the step edge directions [2]. A Wheatstone bridge design was used in order to get rid of common perturbations, such as temperature drift. The measured AMR curves could be compared to the expected behaviour considering the Stoner-Wohlfarth model for coherent magnetization reversal. In order to achieve a higher sensitivity, thus the targeted lower detectivity, several parameters were considered, such as LSMO film thickness, LSMO deposition temperature, vicinal angle of the substrates and design of the electrical contacts. Dedicated electronics readout and gradiometric configuration were considered. The lowest detectivity at 310K was 1 nT∙Hz-1/2 at 1 Hz and 300 pT∙Hz-1/2 at 1 kHz in a single-layer sensor without using any performance enhancing techniques such as magnetic flux focusers or modulation techniques [3]. Such AMR sensors are promising for biomedical applications where small size devices are needed at low frequency. ---------------------------- [1] L. Méchin, S. Wu, B. Guillet, P. Perna, C. Fur, S. Lebargy, C. Adamo, D.G. Schlom, J.M. Routoure, Experimental evidence of correlation between 1/f noise level and metal-to-insulator transition temperature in epitaxial La0.7Sr0.3MnO3 thin films, J. Phys. D: Appl. Phys. - Fast Track Communication 46 202001 (2013) [2] P. Perna et al., Engineering Large Anisotropic Magnetoresistance in Half-Metallic Manganite Films at Room Temperature, Adv. Funct. Mater., 27, 1700664 (2017) [3] L.G. Enger et al., Sub-nT resolution of Single Layer Sensor Based on the AMR Effect in La2/3Sr1/3MnO3 Thin Films, IEEE Transactions on Magnetics 58 (2) 4001204 (2022)

Authors : Izel Perkitel1,2, Ismail Altuntas1,2, Ilkay Demir1,2
Affiliations : 1.Nanophotonics Research and Application Center, Sivas Cumhuriyet University, 58140 Sivas, Turkey 2.Department of Nanotechnology Engineering, Sivas Cumhuriyet University, 58140 Sivas, Turkey

Resume : Quantum cascade lasers (QCL) are laser devices based on inter-subband transitions in semiconductor heterostructures. QCLs are ideal candidates for the mid to far-infrared spectral region, as the emission wavelength is determined by the layer width and array and not by the bandgap. QCLs have been of major interest for a range of industrial applications, including infrared imaging and spectroscopy, as well as various defense applications such as range detection and free-space optical communications. The superlattices based on the InGaAs/InAlAs heterostructure are mostly used in the construction of QCLs. The emission wavelength of lattice-matched InGaAs/InAlAs QCLs with InP substrate covers the infrared region from 3.5 to 24 μm and this gives them the opportunity to use them in applications in chemical and biological sensing or spectroscopy. A particularly promising area of application for QCLs is gas detection in the first atmospheric window (2.9-5.3 µm). Besides line-of-sight telecommunications, military countermeasures based on emissions in the first atmospheric window are also of interest. Laser realization within this region is particularly difficult due to the large conduction band discontinuity (∆Ec) required. The most mature material system used for short wavelength QCLs is the strain-compensated InP-based InGaAs/InAlAs. The QCL core contains hundreds or even thousands of thin layer repeats with a thickness in the 0.5–10 nm range. The growth of QCLs is crucial in terms of alloy composition, layer thickness, and hetero-interface quality of hundreds of ultrathin epitaxial layers. In the case of such complex structures, molecular beam epitaxy (MBE) is often used because it provides a specific composition in individual layers and very high-quality interfaces between them. Therefore, epitaxial growth of such layers with the metal-organic vapor phase epitaxy (MOVPE) technique is very difficult and it is important to find the optimal technological parameters. Growth kinetics depend on various factors such as flow rate of precursors, process pressure, and temperature, and they strongly affect the growth of individual layers. However, due to the high vacuum working processes, the MBE technique has the low QCL production capacity and high QCL cost. Therefore, another competing technique MOCVD was used to grow high quality QCL wafers with high yield. There are few studies in the literature about the effect of inter-layer transition time on quantum well, multilayer structures and lattice-match InGaAs/InAlAs QCL. However, transition time studies have not been performed for strain-compensated QCL structures to the best of our knowledge. In this study, we will examine the optimization studies of the combination of Si-doped and undoped inter-layer transition time in the strain compensated In0.67Ga0.33As/In0.36Al0.64As QCL structure grown on InP substrate by MOVPE. After growth, the crystal quality and thickness sensitivity of the samples will be investigated with a high resolution X-ray diffractometer (HRXRD). Optical transitions in QCL active region structures will be determined by photoluminescence measurements. In addition, optical interband transitions will be calculated with the Nextnano simulation program and comparison between experiment and theory will be investigated.

Authors : D. J. Rogers1, T. Maroutian2, E. V. Sandana1, F. H. Teherani1, P. Bove1, P. Lecouer2
Affiliations : 1. Nanovation, 8 route de Chevreuse, Châteaufort, 78117, France. 2. Centre for Nanoscience and Nanotechnology, CNRS & Université Paris-Saclay, Palaiseau, France

Resume : In order to meet the requirements for future optical communication systems, optical circuits have to be cheaper, smaller, less power hungry and deliver ever-growing data rates. It has long been proposed that silicon photonics, due to compatibility with large volume CMOS fabrication processes, has a unique potential to deliver ultra-compact optoelectronic chips meeting these requirements. Although there has been significant progress in the development of silicon photonics over recent years, handling the multiple wavelengths that arrive simultaneously through optical fibers remains a significant challenge. A potential solution is to integrate the superior nonlinear and amplification performance of Yttria-Stabilised Zirconia (YSZ) with Si photonics. This offers the perspective of simultaneously combining frequency comb generation and light amplification in the same chip. In order to achieve high performance, however, excellent crystalline quality is required for YSZ films on silicon. Unfortunately, this is difficult because of the amorphous native oxide layer which forms spontaneously at the surface of the silicon and thus prevents epitaxial growth. In this work we explore possibility of integrating epitaxial YSZ on silicon through Epitaxial Lift-Off (ELO). ELO is based on the use of a sacrificial epitaxial buffer layer between the substrate and the layer to be transferred. This underlayer acts as both a crystallographic template and a sacrificial release layer. There is an epitaxial relationship between this underlayer and both the single crystal substrate and the layer to be transferred. The template layer is chosen so as to be more susceptible to chemical etching than the layer to be transferred such that preferential dissolution can be achieved. ELO offers several advantages over other lift-off techniques. In particular, it reveals the pristine epitaxial interface of the overlayer, which is very smooth and thus amenable to Van der Waals bonding on a new host substrate. This kind of direct fusion bonding requires no interfacial bonding layer and thus can offer excellent electrical, thermal and optical coupling to the new host. In this study we chose to adopt zinc oxide (ZnO) as the sacrificial template layer because it is readily chemically etched and because it is a compliant material which can readily form an epitaxial relationship with significantly mismatched substrate. In previous work ELO of YSZ was performed using ZnO coated c-sapphire substrates [1]. In this work we employ ZnO-buffered YSZ(111) substrates in order to profit from the superior epitaxial quality on this substrate. [1] Use of Sacrificial Zinc Oxide Template Layers for Epitaxial Lift-Off of Yttria-Stabilised Zirconia Thin Films D. J. Rogers et al. Proc. of SPIE 11687 (2021) 116872C-1

Authors : M. Khokhlova1,2 , Y. Abhishek1 , K. Boumediene2, W. Prellier1
Affiliations : 1. Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN, UNICAEN, 6 Bd Marechal Juin, F-14050 Caen Cedex 4, France 2. Normandie Université, UNICAEN, BIOCONNECT, 14000, Caen, France

Resume : Thin flms of oxides were grown on glass substrates using pulsed laser deposition (PLD) technique and characterized by atomic force microscopy (AFM), X-ray diffraction ray (XRD), scanning electron microscopy (SEM), and Water Contact Angle (WCA) measurements. The growth of human bone marrow mesenchymal stem cells (hBMMSCs) was studied on these films for different periods. Their adhesion, proliferation, and di􏰁erentiation were assessed by di􏰁erent techniques, including SEM, differentiation staining, and reverse transcription polymerase chain reaction (RT-PCR). The data obtained suggest that vanadium oxide impairs normal healthy cell development and inhibits the proliferation of hBMMSCs and their osteogenic and chondrogenic differentiation. These results provide new information on the cytotoxicity of vanadium oxides to human stem cells and offer opportunities for a deeper understanding of the use of oxide thin films for medical applications.


Symposium organizers
Achim TRAMPERTPaul-Drude-Institut für Festkörperelektronik

Hausvogteiplatz 5–7, 10117 Berlin, Germany

+49 30 20377 280
Charles CORNETFOTON laboratory – INSA Rennes

INSA Rennes, 20, Avenue des Buttes de Coësmes, CS 70839, F-35708 Rennes Cedex 7, France

+33 (0)2 23 23 83 99
Frédéric LEROYAix-Marseille Université

CINaM - Campus de Luminy - Case 913 - 13288 Marseille Cedex 9, France

+33 (0)660362824
Gavin BELLUniversity of Warwick

Department of Physics, Coventry CV4 7AL, UK

+44 24 7652 3489